BEDFORD, N.H., NOV. 1 -- Five Democratic presidential contenders held a relaxed, congenial discussion of environmental issues for two hours here today, during which they agreed on virtually every topic, including their superiority to their Republican counterparts.

The candidates appeared at a forum sponsored by a coalition of New Hampshire environmental groups whose members include a number of political activists in this state, site of the first presidential primary next February.

None of the GOP presidential hopefuls accepted invitations to the forum, leaving the Democrats a clear field to attack the Reagan administration's record on the environment.

"Their policies might as well be on that garbage barge floating around the ocean," said Sen. Albert Gore Jr. (D-Tenn.).

Gore appeared at the forum along with former Arizona governor Bruce Babbitt, Massachusetts Gov. Michael S. Dukakis, Jesse L. Jackson and Sen. Paul Simon (D-Ill.). Rep. Richard A. Gephardt (D-Mo.) was the only missing Democratic candidate.

The forum took place against the backdrop of the Nuclear Regulatory Commission's decision last week to drop a regulation that Dukakis has used to block the start-up of the controversial Seabrook nuclear power plant on the New Hampshire coast.

The regulation requires that state and local officials participate in drafting emergency evacuation plans for areas within 10 miles of a nuclear power plant. The NRC voted unanimously to consider licenses for reactors on the basis of a utility's evacuation plan alone if state and local authorities refuse to cooperate.

Seabrook is within 10 miles of the Massachusetts border, and Dukakis, arguing that no evacuation plan is feasible, has refused to approve the evacuation plan. That has made him a hero to environmentalists here, one of the many reasons he is considered far ahead of any of his Democratic rivals in New Hampshire.

Asked a question today about acid rain, Dukakis first referred to the nuclear power controversy, saying, "We're going to do everything we can to stop Seabrook."

The other candidates also drew applause from an audience of about 300 by making equally strong anti-Seabrook statements.

On this and other issues -- including acid rain, ground-water pollution, population growth, energy policy and toxic waste -- there was broad agreement among the five Democrats. All supported regular international summits on environmental issues and said "polluters should pay" for the cost of cleanup programs. None of them offered specific plans to finance expansion of government environmental programs, although Babbitt reiterated his call for higher taxes to reduce the deficit.

With nothing to argue about, the discussion went smoothly as the candidates sat at a large, round table answering questions from a panel of four experts and moderator Sander Vanocur of ABC News. Babbit praised Dukakis for his position on Seabrook and Gore and Simon complimented Babbitt for his work on ground-water pollution.

Jackson stressed the need for prevention of new pollution problems and Simon called for increased spending on environmental research.

Gore, who has attempted to separate himself from the others by taking more conservative positions on defense policy, did not move to the right on environmental issues in the room filled with environmental activists.

"You don't sound so conservative, Al," Babbitt said after Gore answered the first question.

Judging by the audience's reaction, Gore may have had a slight advantage in terms of impact, but none of the candidates hurt himself.

"They all impressed me in terms of knowledge, preparation and commitment," said Ian Nisbet, an environmental consultant and one of the questioners. "They all said the right things."

"Clearly, the Democratic Party won because everyone of these guys showed he is preferable to the present administration," said Alden Meyer, executive director of the League of Conservation Voters.

One Republican candidate, Alexander M. Haig Jr., was here briefly today, holding a news conference before the candidates' forum. He said a previous commitment in New York prevented him from participating in the forum.

Haig said he was not defending Reagan administration environmental policies, but he supported the NRC's Seabrook decision and said Dukakis' refusal to cooperate in drafting an evacuation plan was "not an environmentally responsible position."

Among the GOP candidates, only Rep. Jack Kemp (R-N.Y.) supports Dukakis' stand on Seabrook.