GOFFSTOWN, N.H., NOV. 21 -- The first New Hampshire forum for all six Democratic presidential candidates today turned into a matinee version of Saturday Night Live.

Rival demonstrations, backstage feuding and a disruption by a man who shouted anti-Semitic slogans at the state Democratic convention consumed enough time that the scheduled question-and-answer sessions for the six hopefuls and a panel of reporters had to be canceled. After 2 1/2-hours of planned and unplanned tumult, with occasional intervals of speechmaking by the contenders, no clear winner emerged in the first big event here before the Feb. 16 leadoff primary.

The only loser was the image of a state Democratic Party that has scored few victories in recent elections.

But state party Chairman J. Joseph Grandmaison said the time-consuming demonstrations were a sign of the party's health. "When you look at the enthusiasm in this hall, that's the important thing," he said.

The candidates also appeared unbothered by the cancellation of the forum.

"It's a lot of fun and a lot of spirit. I like it," said Massachusetts Gov. Michael S. Dukakis.

Supporters of every Democratic candidate except Jesse L. Jackson had made major efforts to turn out hundreds of people, either by electing delegates or infiltrating ringers into the gymnasium at St. Anselm's College. At the end of a long afternoon, it was not obvious what Dukakis, who is leading in early polls in the state, or his rivals, Sens. Paul Simon (Ill.) and Albert Gore Jr. (Tenn.), Rep. Richard A. Gephardt (Mo.) and former Arizona governor Bruce Babbitt, had gained for their expense and exertion.

The trouble began Friday night when rival bands of young staff members and volunteers descended on the gym, armed with extension ladders and staple guns, and fought a pitched battle over space for their banners and posters. "It was a real zoo," said state Vice Chairman Scott Williams, describing pushing and fist fights.

Grandmaison summoned leaders of the six campaigns to the scene, showed them the shambles and enforced a division of wall and rafter space.

The entrance of the six candidates this afternoon produced another battle of bands, chants, klaxons and whistles, as each campaign sought to demonstrate support among the 1,100 delegates and the spectators crowded into the gym. Left shivering in the cold wind outside was a band of New England college students with signs urging former senator Gary Hart of Colorado to return to the contest he abandoned last spring after reports of his association with Miami model Donna Rice.

While the rival demonstrators were chanting for their candidate, there was a spat involving Gore and Grandmaison. The party chairman was angered when Gore was late in arriving at the convention site and kept him cooling his heels outside the hall until he was introduced. That was after all the others had spoken.

Simon began the afternoon by defending the New Hampshire and Iowa primaries. Far from "distorting the process," as Gore had suggested in a television interview the six had taped earlier today in Massachusetts, these early contests in small states force candidates to face "the real problems of real people," Simon said.

Simon and Gephardt shorthanded their policy arguments into cheer-provoking lines and took frequent swipes at President Reagan. Pledging an activist administration, Gephardt said, "No more cue cards; no more sleeping presidents. Wouldn't you like to be proud of a president again . . . who throws out the value of greed and brings back the value of caring?"

Jackson, who had the fewest signs and supporters in the gym, told the attentive audience that the demonstrations that were meaningful to him were those of farmers facing foreclosure, workers facing layoffs, of AIDS victims and civil rights protesters.

Dukakis, whose welcoming demonstration was less overwhelming than his lead in the polls in this state, touched off a minicontroversy with Gephardt. Pledging to make "the tough choices" as president, Dukakis said he would pick "star schools over Star Wars," adding, "That's my line."

Gephardt had used the same phrase in his speech. And a Gephardt spokesman, Mark Johnson, said the "star schools, Star Wars" phrase actually belonged to Sen. Edward M. Kennedy (D-Mass.) and had been borrowed by both Dukakis and Gephardt.

Dukakis' closing comments were all but drowned out by a loud-voiced demonstrator, shouting anti-Semitic slogans at the governor, whose wife, Kitty, is Jewish, and the demonstrator persisted long after Dukakis left the stage.

Babbitt, who had tried to intervene in that situation, finally got his turn at the microphone and urged New Hampshire Democrats to "defy the conventional predictions" as they have done in four of the last five primaries. The longshot from Arizona, summarizing his argument that the "budget deficit crisis" can be solved only by raising taxes and basing benefits from entitlements programs in part on the income of the recipients -- so called means-testing -- asked New Hampshire to "vote for straight talk and honesty about our future as Americans."

Gore changed his tactics during the day. He steered away from repeating criticism of the importance attached to the Iowa and New Hampshire contests and confined his remarks before the New Hampshire Democrats to an attack on Reagan administration policies.

"They made promises they could not keep," he said. "They offered feel good illusions."

But Gore did repeat a mild jab at Dukakis, saying, "We need a Democratic president with experience in foreign policy and national defense to deal with the Soviet Union."

Staff writer Lloyd Grove and researcher Colette T. Rhoney contributed to this story.