MANCHESTER, N.H., FEB. 15 -- The seven Democratic presidential contenders wound up their campaigning for Tuesday's New Hampshire primary tonight, with Massachusetts Gov. Michael S. Dukakis (D) anticipating a big victory and several of the others wondering if this is the end of their 1988 road.

Phone interviews with 963 likely voters from Saturday through today by The Washington Post and ABC News continued to show an extremely tight race for second place between Rep. Richard A. Gephardt of Missouri, the winner of last week's Iowa caucuses, and Sen. Paul Simon of Illinois, who finished a step back there.

The survey gave Dukakis 41 percent, Simon 17, Gephardt 17, Jesse L. Jackson 5, Sen. Albert Gore Jr. of Tennessee 7, former Arizona governor Bruce Babbitt 5, and former Colorado senator Gary Hart 5.

Among the 408 likely voters interviewed this evening, the pattern was essentially the same, with Dukakis at 47 percent, Gephardt at 16 percent and Simon at 15 percent.

As he made a last sweep through the state, Dukakis warned his supporters against overconfidence. "In the closing days of the campaign," he said in Claremont, "things always tighten up. I'm sure they will in this one."

But there was no visible chink in Dukakis' armor. After 10 years as governor, he is a familiar figure in the four of every five New Hampshire homes that receive Boston television. And his leadership in the fight to block a start-up of the Seabrook nuclear power plant has made him a hero for many liberals and environmentalists in this state.

Today, the organization he has assembled over the past nine months was expanded by hundreds of Massachusetts state employees and their families, using the President's Day holiday to make final phone calls to New Hampshire voters and fill almost every shopping center parking lot and downtown thoroughfare with people carrying Dukakis signs.

If Dukakis' numbers hold up, it would be the biggest margin of victory for any contested Democratic candidate since the New Hampshire primary became a major political event in 1952. His numbers would far eclipse the 11-point lead Estes Kefauver won over President Harry S Truman in 1952, and the margins achieved by President Jimmy Carter over Sen. Edward M. Kennedy (Mass.) in 1980, Hart over Walter F. Mondale in 1984 and Sen. Edmund S. Muskie (Maine) over Sen. George McGovern (S.D.) in 1972, all of which fell between 9 and 10 points.

The victory would go a long way toward erasing whatever minor damage Dukakis received in the national polls from his close third-place finish in Iowa and provide a boost for his challenge to Gore and Jackson, who have greater strength in the South than in Iowa or New Hampshire.

Dukakis, the best-financed of the Democrats, is already a strong competitor of Simon in Minnesota and of Gephardt in South Dakota, the major contests on Feb. 23, as well as being the favorite in the Maine caucuses and Vermont primary, which also precede the March 8 southern-dominated "Super Tuesday" voting in 20 states.

Both Simon and Gephardt spent themselves into debt to outdistance Dukakis in Iowa and challenge him here in his backyard. Neither is so squeezed that he would likely withdraw before the next round of voting in the Midwest on Feb. 23 or Thursday night's debate in Dallas. But aides acknowledged that fund-raising will become much harder for the candidate who finishes in third place here, especially for Simon if he should again be beaten by the St. Louis congressman.

Today, however, they were relentlessly upbeat as they stoked the enthusiasm of their supporters at a series of rallies across the populous southern tier of the state.

Gephardt was accompanied by House Majority Leader Thomas S. Foley (Wash.), who defended his colleague from charges of philosophical inconsistency Simon had made in stump speeches and TV ads during the past week and which Gore and Babbitt echoed in the Saturday candidates' debate.

"I absolutely reject the notion that Dick Gephardt has flip-flopped on issues," Foley said. "He's stayed consistent and strong in his values . . . . I'd be embarrassed if after 25 years in Congress, I had never changed my position on anything and was some kind of robot."

Gephardt took a final swing at Simon, who has criticized him for supporting the 1981 tax cut, by arguing that if Simon's opposition view had prevailed, "the average family in New Hampshire would have paid an additional $3,900 in taxes over the past six years."

For his part, Simon took his focus off Gephardt and jabbed at Dukakis, suggesting that New Hampshire Democrats "assert their independence" by confounding the polls and proclaiming that "America needs more than just a skillful manager," as he categorizes Dukakis.

Gephardt and Simon campaign officials in Washington said they had raised $400,000 and $200,000, respectively, in the past week, capitalizing on their first- and second-place finishes in Iowa. But both are in debt -- an acknowledged $250,000 in Gephardt's case and twice that in Simon's. Both have major fund-raisers scheduled for the next few days and their success is obviously contingent on their show of strength here.

Jackson's goal here is to break into double digits, as he did in Iowa, as part of his effort to expand his political base beyond blacks and liberal activists. "In this state," he said, "our campaign is showing growth and acceptance. But this is the second game of a 50-game schedule."

Gore campaigned briefly here today and predicted he would do "better than people expect" in Tuesday's voting.