WASHINGTON (AP) _ Opponents of the Seabrook nuclear power plant charged in court today that the Nuclear Regulatory Commission failed to make adequate provision for public safety before approving the plant on the New Hampshire seacoast.

But lawyers for the NRC and the Public Service Company of New Hampshire told the U.S. Court of Appeals the commission made sure the public would have substantial protection. And a representative of Seabrook's operator said it is impossible to tell how much protection would be adequate before a nuclear accident occurs.

A three-judge panel of the court heard arguments on the petition of the attorney general of Massachusetts and two citizens' groups to revoke the license on grounds that the NRC violated its own procedures.

The arguments focused on required emergency plans for people living in 17 New Hampshire communities and six in neighboring Massachusetts. Opponents said the plans won't work.

''The commission did not make a judgment on whether or not there were adequate evacuation plans,'' Robert A. Backus, attorney for the two private environmental groups, told the court.

''They basically made a judgment without looking at the evidence,'' said John Traficante, assistant Massachusetts attorney general. ''We are not saying they drew the wrong line. We are saying they drew no line.''

Traficante argued that the commission relied on ''a check list that doesn't have any teeth.'' On this basis, he said, it ''could approve a site on 42nd and Broadway'' in New York.

John F. Cordes Jr., representing the NRC, said the commission assured that there would be ''a full measure of planning'' for an emergency and that this ''would be substantial protection'' for the public.

''This is not a secret approach,'' he said. ''It's nothing mysterious.''

Thomas G. Dignan Jr., representing New Hampshire Yankee, Seabrook's operator, said ''The adequacy (of an evacuation plan) is something that will never be deteremined at a nuclear site until the day of the accident.''

Seabrook was licensed by the commission in March after nearly two decades of court challenges and thousands of arrests in mass demonstrations.

The plant began regular operations on August 19.

On Monday, about two dozen opponents of the plant gathered in front of the White House for another demonstration.

''President Bush has seen fit to draw a line in the sand in the Middle East; it is time he draws a line against the nuclear mess in this country,'' said Stephen B. Comley of Rowley, Mass., executive director of the anti- nuclear group We the People, Inc.

Comley, noting that the plant lies only 18 miles from the president's vacation home in Kennebunkport, Maine, said, ''It is about time Mr. Bush started listening to the people of this country ... instead of his pro-nuclear chief of staff,'' former New Hampshire Gov. John Sununu.

The demonstrators drove to the White House in a caravan bearing car-top signs. One read, ''Congress: Protect U.S. Democracy.'' ''Investigate the Nuclear Regulatory Commission'' and ''Danger. Seabrook Nuclear Zone. No Evacuation Possible.''

The largest, a 12-foot sign atop a truck, read simply ''Danger.''

Comley and another demonstrator tried to attach an even larger sign to the White House fence, but a National Park Police officer, J.D. Reardon, stopped them.

Park Police spokesman Kevin Chittick said signs cannot be attached to or leaned against the fence because they obscure the view of Secret Service personnel responsible for security inside the White House grounds. However, demonstrators who have obtained a permit may carry signs of limited size on the sidewalk outside the fence, he said.

On their way from New Hampshire the demonstrators stopped at Three Mile Island in eastern Pennsylvania, site of the nation's worst commercial nuclear accident on March 31, 1979. Comley said they also planned demonstrations outside the courthouse and the NRC headquarters.