"The numbers are definitely on our side, " brags Walt Witich, a Democratic Party political operative.

A GOP counterpart, Steve Letterer, responds, "There's a Republican wind blowing out there."

Both politicos are talking about the same thing-this year's bevy of congressional races, 33 in the Senate and 435 in the House of Representatives, to be exact.

The stakes are big; for the first time this century the two houses have been under split control for more than two consecutive years. Both sides think they can, at the very least, make strides towards changing that around. And this strange presidential year, both sides may be right.

Democrats like Witich, research director of the party's senatorial campaign committee, are banking on the odds. For the first time in three senate elections, Republicans up for reelection outnumber Democrats-19 to 14. With more ducks to shoot at, Democrat pols think they have a chance to win back the control of the senate they lost in 1980, although because they are down 55-45, the chances of this are slim.

Republicans, conversely, hope that they will be able to ride the coattails of Ronald Reagan and his economic recovery and bite into the Democrats 268-167 advantage in the House. Letterer has just returned from a nation-wide trip with Rep. Guy Vander Jagt (R-Mich.), chairman of the National Republican Congressional Committee, and says he found "people optimistic about the future and waiting to vote Republican. It's a complete turnaround from 1982, when everyone was depressed about the economy."

But the fanciful scenarios that dance through a politico's head, can be a far cry from what is likely. No one expects both the election of a Democratic president and, say, a turn to the right in Congress. More to the point, no one is really expecting the Republicans to make any major inroads into the Democratic majority in the House. The real action is going to be in the Senate, where a shift of six seats could return the Democrats to the top perch and return important committee chairmanships to senators like Sam Nunn (Armed Forces), Edward M. Kennedy (Labor and Human Resources), and Lloyd Bentsen (Environment and Public Works).

"The absolute best the Republicans can hope for in the House is to gain a few of the 26 seats they lost in 1982, and even that won't give them a working coalition with conservative Democrats," says Norman Ornstein, a political science professor at Catholic University in Washington, D.C. "But in the Senate they face a real challenge," Ornstein adds.

"There's a tough situation ahead of us," admits one Republican National Committee strategist, Ceci Cole. "Our incumbents are vulnerable and half of the Democratic incumbents are from bedrock Democratic states."

Democrats are especially confident because, of the 19 Republican Senate seats up for grabs, eight incumbents won their elections with 55 percent or less of the vote. The conventional wisdom held by full-time pols is that 55 is the magic number for determining whether a seat is vulnerable or not.

While Democrats have numbers on their side, however, Republican candidates in the country have a few things going for them. Not the least of which is that, for all the trends moving in their direction, the Democrats still have a lot of ground to make up.

Even in a good year, a swing of six seats is a lot-especially if they come from a party that far outdistances the other in terms of money and organization.

As a group, the Senate Republicans are now projected to outspend their Democratic opponents by an up to 10:1 margin and will reach in each state the maximum dollar figure a national party organization can legally spend. In the 1982 congressional races, the Republicans outspent the Democratic campaign committees by 4 to 1, and while the Democrats are expected to do better this time out, they won't even be able to come close to matching the GOP war chest.

What's more, even the best of Dems are envious of Republican organizational skills. Ornstein says the Republicans are better at spending their money. That is, because their funding organizations are tightly centralized, they can carefully target funds towards close races. Democratic funding organizations, by contrast, are more decentralized and those candidates who need large sums of cash are often left in the lurch while runaway winners sometimes find huge chunks of money in their treasuries when their campaigns are over.

Democrats have already unleashed a strong challenge in North Carolina and Iowa, where the most interesting races of the year have begun to shape up.

The celebrated North Carolina race--which some say will overshadow the Presidential race in rhetoric if not reality--pits the scourge of right wing conservatism, Sen. Jesse Helms, against Democratic Gov. James B. Hunt, Jr. Polls taken late last year put the popular Hunt-progressive in Southern terms--ahead of Helms by as much as 20 points, though more recent polls show that Helms has closed the gap.

In what promises to be one of the most expensive races in the country, Democrats hope to counter superior Republican fundraising ability with a flood of Black voter registration, which is likely to aid Democratic candidates throughout the South.

In Iowa, Republican incumbent Roger W. Jepsen, has also closed a polling gap on his Democratic challenger Rep. Tom Harkin. But Iowa seems to have a distaste for incumbents--no senator has won a second term there since 1966 Senate Majority leader Howard Baker's decision to step down in Tennessee induced the popular Democrat Rep. Albert Gore Jr. to make a bid for the seat. Gore will probably benefit from a fractious Reublican primary, in which an extreme right-wing religious leader has been viciously attacking his moderate foe.

Texas, where Sen. John Tower is retiring, presents a different situation, because a difficult Democratic primary is expected before the winner faces likely Republican nominee Rep. Phil Gramm. Tower squeaked by with 50 percent in his 1978 election.

Democrats would particularly like to unseat prominent Sen. Charles H. Percy of Illinois, chairman of the Foreign Relations Committee. Although a moderate on social issues, Percy has stood quietly, but staunchly, behind President Reagan's economic program. He faces a strong challenge from the right, from the more uniformly conservative Rep. Tom Corcoran, in what will probably be the only GOP primary for an incumbent.

The most attractive Democratic candidate in Illinois would probably be Rep. Paul Simon, who is stepping down from the Congressional seat he has held for ten years. But Simon, whose vocal support for higher education funding as chairman of the House Subcommittee on Post-secondary Education has helped win him respect from liberals, must overcome three rivals in the Democratic primary.

Other vulnerable Republican Senators include Thad Cochran of Mississippi, who, like Helms and Jepsen, has trailed his Democratic challenger in polls, Gordon J. Humphrey of New Hampshire, and Rudy Boschwitz of Minnesota. Observers say Walter F. Mondale, also from Minnesota, could play a role in Boschwitz's fate, if he lands the Democratic presidential nomination. Mondale's ticket would rouse a strong Democratic turnout at the Minnesota polls in November.

Republicans, on the other hand, could mount particularly strong challenges in Rhode Island and West Virginia, but they have not yet been able to persuade their first-choice candidates to challenge the Democratic incumbents.

In Rhode Island, everyone, including GOP officials, has said that Rep. Claudine Schneider will not run for the seat held by four-term Sen. Claiborne Pell. Everyone except Schneider herself, that is, who says she is still pondering a shot at the Senate.

GOP attempts to draft former West Virginia Gov. Arch A. Moore Jr. in the race against present Gov. John D. Rockefeller IV have so far been unsuccessful. Moore could provide Rockefeller with a tough fight for the seat from which long-time Senator Jennings Randolph is retiring.

House races will surely be less tumultuous than the Senate because less is at stake. Republicans would have to make extraordinary gains to challenge the majority control Democrats have held in the House for 28 years. And in House races, where issues are generally less important than personality factors, nationwide trends tend to blur in significance. Still, insiders who talk about the races make a few basic points:

Republicans and Democrats agree that the 52 Democratic freshmen form the critical group in the House elections.

Voting trends show that the country is becoming more sympathetic to incumbents after a period of hostility spurred by Watergate. Republicans want to nip the Democratic freshmen in the bud before they gain the vaunted status of political old-timers.

Republican strategy, according to Republican Lotterer, is to cast the races as a "Reagan vs. Mondale-O'Neill" contest. Lotterer says that the Democratic freshmen have simply fallen in lockstep behind effective Democratic party leader Rep. Thomas P. O'Neill Jr. (D-Mass.), whose old-fashioned liberalism he thinks is out of favor with much of the electorate.

But Johnson of the Democratic Congressional Campaign Committee argues that "our people aren't ideological like the 52 Republican freshmen who won in 1980."

14 of those 52 Republicans fell in 1982, but Johnson says the Democrats will not suffer similar losses because "our freshmen won't rise and fall with Mondale."

An important factor working against House Republicans is the scant likelihood that they will assume majority status within the next three or four elections, observers say.

"It's awfully depressing to know you may not be in the House majority, even in your lifetime," says Ornstein.

Ornstein noted the retirement of respected Republican New York representative, Barner B. Conable Jr., as an example of about a halfdozen senior House GOP members who are stepping down this year.

Democrats in national organizations and those in Congressional offices cite the new Democratic "media center"-at which candidates can produce commercials for one-third the cost charged by independent media firms--as a factor in their chances. Republicans have long had such a production facility, and Democrats hope the center will alleviate some of their financial woes.

Some of the interesting races involve rematches between House freshmen and the Republican incumbents they defeated, although in this area too, a Republican weakness is evident.

Republican difficulty in convincing defeated Republicans to run again has forced the GOP to cool its rhetoric. So after the Democrats picked up 28 seats in the 1982 elections, GOP spokesmen talked of 20 more rematches. These days, Vander Jagt boasts of a possible 10.

A few of the lively rematches:

Democratic freshman Bruce Morrison of Connecticut, at 39 seemingly too young for his New Deal Politics, faces Larry DeNardis, an exponent of the Italian-American machine politics which has dominated his New Haven district since the fifties. Morrison nipped DeNardis 50 to 49 percent in 1982.

Freshman Lane Evans of Illinois faces Kenneth G. McMillan, a hardline conservative who won the 1982 GOP primary over then Rep. Tom Railsback, largely because Railsback was implicated in the Paula Parkinson sex scandal. in Illinois, along with Texas, the Democrats expect to make their biggest House gains, and Evans' district, which is fairly representative of Illinois outside of Chicago, is a watermark for Democratic chances.

One of the most expensive and prominent House races will pit Democratic Rep. James K. Jones (D-Okla.) against the winner of a Republican primary in which both contenders have already spent more than $1 million each. Jones parallels the conservative Democrat, but as Chairman of the House Budget Committee, he has done as much as any congressman to dismantle the Reagan economic program.