WHILE President Reagan was on another California vacation, while Vice President George Bush was fishing in Wyoming, the Democrats were in Atlanta, working. They sought to unify the party, to define their message, to prove they are capable of leading the nation into the 1990s, and they did all three.

Democrats left their convention united and confident of victory in November, and rightly so. They eloquently presented the case against "Four more years" of Republican rule. And their standard bearer, Gov. Michael S. Dukakis, looked presidential as he promised to help bring "a new era of greatness" to America.

Maybe some day George Bush will discover what he believes in or uncover "that vision thing" they say he's searching for. Mike Dukakis knows what's wrong with America, and how to fix it. Better yet, he has found a number of points of weakness on the Republican side, and at each point of attack, he has a solution of his own to offer. As James Reston has put it, Mike Dukakis' answer to the taunt, "Where's George?" is, "Right behind the eight ball."

He has a vision of America where graft and corruption aren't tolerated. Where the president tells the truth, and requires his subordinates to remain above reproach. Bush, for eight years, has remained silent about his corrupt associates.

Ronald Reagan and George Bush have spent eight years running against the government they run. They've shown utter contempt for the institution they head. Dukakis promises to "restore the pride in government" that has waned under Reagan.

DUKAKIS has managed to wrestle away from the Republicans one of their oldest and proudest themes: fiscal responsibility.

After eight years of record budget deficits, America needs a "frugal man" in the White House, the Bay State governor said. Mike Dukakis has balanced nine state budgets and will work tirelessly to bring down the deficit.

The Democrats left town without promising to raise taxes. And Mike Dukakis left Atlanta looking very little like George McGovern, Walter Mondale and other Democratic losers.

Reagan says "You'll never hear that 'L' word--liberal--from" Dukakis, and he's right. Dukakis says this election "isn't about ideology." George McGovern isn't on the ballot this year. And George Bush won't be facing Fritz Mondale come November. He'll be facing a competent, hardworking statesman not far from the mainstream of American politics. Republicans won't win by pinning labels on Dukakis.

The Democratic nominee says this election is about competence, and that's bad news for George Bush. If the American people examine Bush's record of inaction, his silence on civil rights, the environment, education and the deficit from 1980 to 1987, they're liable to send him packing.

Mike Dukakis and the Democrats also have shown that the Republicans have no monopoly on optimism.

"We believe there are no limits to what America can do," Dukakis told delegates at the convention. No longer the party of doom and gloom, the Democrats sound positive about the future. And they should: after eight years of Reagan, the Democrats appear headed for victory come November.

REPUBLICANS will gather in New Orleans August 15-18 to present their case to the American people. Already trailing Dukakis badly, they desperately need to close the gap in the polls.

The Democrats spent four days bashing Bush and it paid off. Bush is an easy target: a bumbling and boring rich boy with a penchant for looking silly. A man disliked by an amazing percentage of the American electorate, if the latest polls are to be believed. So what are the Republicans to do?

Republicans will crow about low inflation and low unemployment. They'll claim full credit for the thaw in relations with the Soviet Union. And they'll talk a lot about the bad old days when Jimmy Carter was president and gas cost nearly a $1.50 a gallon.