MANCHESTER, N.H.--After enduring the culmination of months of campaigning, voters here will cast the country's first primary election ballots of the 1992 presidential campaign today.

Just less than half of New Hampshire's 561,000 voters are expected to go to the polls to choose from the 25 Republicans, 36 Democrats and one Libertarian on the ballot.

President George Bush and former Massachusetts Sen. Paul E. Tsongas are expected to win their primaries, finishing ahead of conservative commentator Pat Buchanan and Arkansas Gov. Bill Clinton, respectively.

As important as the outcome, however, is the margin of victory in those races.

Depending on the success at the polls today, the campaigns of Iowa Sen. Tom Harkin, Nebraska Sen. Bob Kerrey and California Gov. Edmund G. "Jerry" Brown could be seriously crippled.

A Gallup poll conducted for CNN and USA Today over the weekend put Tsongas at 40 percent of the Democratic total, with Clinton at 20 percent, Harkin and Kerrey tied at 10 percent each and Brown at seven percent. Six percent said they would write in New York Gov. Mario Cuomo.

The poll was conducted before Sunday night's Democratic debate.

The same poll, which has a plus or minus three-percent margin of error, placed Bush ahead of Buchanan 60 to 31 percent in the Republican totals.

Voters over the past two days have said the so-called "pocketbook issues"--taxes, health care, government spending, for example--will weigh most heavily in their minds while voting. Less emphasized, but still significant for voters, are issues like education and the environment.

In a shift in mood from Sunday's debate, Democratic candidates criti- till significant for voters, are issues likeeducation and the environment.

In a shift in mood from Sunday's debate,Democratic candidates criticized each othersharply yesterday, each trying to portraythemselves as the man best capable of beatingPresident Bush in the general elections.

Kerrey, speaking at a health care forumsponsored by the American Associated of RetiredPersons (AARP), called Harkin a "Hulk Hogan" forhis treatment of fellow Democrats. At the forum,Kerrey denied he was a single-issue candidateinterested only in national health insurance.

For his part, Harkin said in his last-minutewhistle-stops yesterday that his candidacy offersa bold break with current economic policy. He alsoasserted that he had the best potential fornational success, a theme that Tsongas repeated inhis address at Phillips Exeter Academy.

Tsongas said that voters should choose his"intellectual integrity" over populist appeals ofthe other candidates.

Clinton, in several appearances yesterday,focused mainly on his own chances for success,despite polls which show him trailing Tsongas bysignificant margin. Citing the still undecidedportion of the electorate--seven percent in mostrecent polls--Clinton said he hoped to win NewHampshire.

Brown, who may be on the last legs of arebel-style candidacy, continued to label all hisopponents as insider politicians in stops aroundthe state yesterday. He also said Sunday's debatewas too polite.