Eleven members of the War Resisters League, arrested last Labor Day as they staged a demonstration on the White House lawn against nuclear arms and nuclear power, were convicted yesterday of refusing to leave.

The verdict climaxed seven days of trial, an unusually long time for what was regarded as a relatively simple case. The verdict left some of the defendants bitter at the lenth to which the government had gone to prosecute the case.

Grace Paley, 55, a teacher at Sarah Lawrence College and a writer of short stories, "What we had been talking about was the noise of war and that armaments are building up, and we step on the grass and that becomes a terrible thing."

According to testimony in the trial, the 11 defendants entered the White House on Labor Day as tourists, took the White House tour, and, as they left the building, stepped over a low chain, walked across the driveway and unfurled a banner. Minutes later a White House policeman approached soem of the demonstrators and informed them that they could not stay where they were.

Precisely what the officer and others who followed said to the demonstrators was a matter of dispute during the trial. The government contended that the demonstrators were given clear and adequate warning to leave. The demonstrators argued that they never received adequate warning and that some believed they had been arrested before they actually were.

Assistant U.S. Attorney Kenneth Reisler argued that even if the demonstrators had been given more time-they were given about five minutes to leave before being arrested-they would have stayed.

The demonstration was planned to concide with a similar protest by War Resister League members in Moscow's Red Square. Although league members were fearful about the fate of the Moscow demonstrators, Soviet authorities broke up that protest without arresting anyone.

Defense lawyers Kathleen Johnson and James R. Klimaski asked Superior Court Judge Donald Smith to waive the presentence investigation normally conducted on each defendant. Smith denied the request, despite Johnson's argument that some of the defendants-those with no prior arrest records-would clearly end up qualifying for probation under District of Columbia procedures.