GOFFSTOWN, N.H., FEB. 13 -- Rep. Richard A. Gephardt (Mo.), the winner of last Monday's Iowa caucuses, was gang-tackled in a televised debate here today by three of his rivals in Tuesday's New Hampshire Democratic presidential primary.

Sen. Paul Simon (Ill.), locked in a close battle with Gephardt for second place far behind Massachusetts Gov. Michael S. Dukakis, got help from Sen. Albert Gore Jr. (Tenn.) and former Arizona governor Bruce Babbitt in the assault on Gephardt.

Dukakis, who shows a widening lead in the latest Washington Post-ABC News poll, drew some flak from former senator Gary Hart (Colo.) and others but was almost as unscathed by the debate as Jesse L. Jackson. Jackson was applauded for saying the "tit-for-tat" exchanges are a symptom of "campaign fatigue."

The Post-ABC tracking poll, taken Wednesday through Friday night, has Dukakis with 40 percent; Gephardt, 16; Simon, 15; Jackson, 8; Gore, 7; Babbitt, 4, and Hart, 3, with 7 percent undecided. Dukakis added six points to his margin over the three previous days.

The League of Women Voters debate in an auditorium on the snow-covered campus of St. Anselm College was barely under way when Gephardt renewed his complaint that Simon's television ads, asking whether voters can "trust" a candidate who has changed his positions on as many issues as Gephardt has, had gone "over the line" in questioning his motives.

Gore said he found it "amusing that Dick Gephardt would react personally to ads from Paul Simon that simply spell out his record." Addressing Gephardt, the Tennessean said, "You ought to respond to the substance of the Simon commercials rather than taking it personally."

Babbitt jumped in to criticize the Missouri congressman's defense of his 1981 vote for the Reagan administration tax bill in a speech to a party dinner in Concord on Friday.

Babbitt said, "After denying his association with the Reagan tax cuts {earlier}, last night he was saying he was the godfather of the Reagan tax cuts. I would call that not just a flip-flop but a triple back somersault with a half-twist."

Gephardt said, "I am beginning to feel that when we're through this, I'll be ready for Bob Dole."

But he was not finished. Gephardt had apologized to Gore at the outset of the debate for comments that William Carrick, his national campaign manager, had made earlier in the week to The Washington Post, calling Gore and his manager, Fred Martin, "the phoniest two-bit bastards that ever came down the pike."

Gephardt blamed them on "the heat of battle" and said he and Carrick regretted them. But when Gephardt later complained that Simon's ads "distorted" his record, Gore said he should recognize that Carrick's attack was far more personal than anything Simon had said about Gephardt.

A moment later, Simon told Gephardt that "you voted for the MX missile seven times, and now you say you're opposed to it. I think it is legitimate to ask what direction you're going."

"Of course, it's legitimate," Gephardt said, "but back in 1948 you {Simon} endorsed Tom Dewey and now you base your campaign on Harry Truman. All of us reexamine principles, and when you say in the television ads, 'Who do you trust?' I do think that goes over the line."

The rancor abated a bit during one lull as the candidates turned their criticisms on the Reagan administration, noting recent revelations about the Central Intelligence Agency's relations with the government of Panama and citing the need to have U.S. allies share more of the burden for defending Europe.

Hart, in particular, turned this portion of the discussion into another opportunity to defend himself against the character questions that have dogged his revived candidacy.

"I hope some day someone will ask Ronald Reagan about his values in presiding over the most corrupt administration in recent American history," he said.

But the candidates quickly returned to the disagreements among them. Recalling the 1984 Democratic debate in Atlanta in which former vice president Walter F. Mondale questioned Hart's "new ideas," Hart asked Dukakis "Where's the beef?" when Dukakis talked of his budget and energy programs.

And Gephardt questioned both Simon and Dukakis on how they could manage to avoid tax increases. "It's a legitimate issue that needs to be answered," Gephardt said. "If you're going to {raise taxes}, say it now; don't say it later."

Gephardt, who said at a Democratic Party dinner here Friday that he is proud of his votes in favor of two Reagan administration tax bills in 1981 and 1986, came under fire for his stand.

"The loopholes you opened up in 1981 you closed in 1986," Dukakis said.

Jackson, who took pains to separate himself from the infighting, told his quarreling colleagues, "You have to have a tough mind and thick skin to run for president. People will say a lot of things about you, but we should address more important issues during this precious hour."

Hart, reminding the audience of his victory here four years ago, said, "I am back in this race and intend to continue." But tonight could have been the farewell appearance for the trailing candidates.

Babbitt virtually acknowledged that that was the case for him. "Let me be blunt," he said. "New Hampshire has the power of life or death over my candidacy. I don't expect to win the New Hampshire primary, and I don't have to win. What I really need from you is simply to send a message."

When Gore endorsed Simon's criticism of Gephardt, it was viewed as a sign that the Tennessean, who has placed all his hopes on the March 8 "Super Tuesday" contests mainly in the South, would rather see the liberal Illinoisan win a ticket south by capturing second place here. Gephardt has the endorsements of many southern colleagues in the House and could pose a more substantial challenge to Gore's base.

The talk in Democratic circles all day concerned Gephardt's decision to lash back at Simon's criticisms and to claim the title of tax-cutter for himself.

Carrick and Ed Reilly, Gephardt's pollster, said in an interview that their nightly surveys show no gains for Simon since he went on the attack. But Reilly acknowledged that the Simon ads are "raising troubling questions about Dick and disturbing the friendly feeling people here had been developing toward him."

Carrick said Gephardt had lost some of his hoped-for victory margin over Simon and Dukakis in the closing days of the Iowa campaign when he came under "double-barreled attack," and had decided not to remain passive in the face of a similar assault here. Tonight, the Gephardt campaign began airing a new ad criticizing Simon and Dukakis.

As for the tax-cutter claim, Carrick said it is "a long-term theme" aimed particularly at Dukakis.