The U.S. Court of Appeals ruled yesterday that the Park Service must allow the District's homeless to sleep in Lafayette Park and on the Mall as part of a demonstration to underscore the plight of the city's street people.

In a 6-to-5 ruling, the 11-member appeals panel reversed an earlier District court decision and gave the go-ahead to the Community for Creative Non-Violence to have the homeless sleep in tents at both sites during a seven-day, round-the-clock demonstration.

However, CCNV leader Mitch Snyder said that the group has not decided whether it will carry out the demonstration, which originally was planned for last December.

Snyder said he thought it might be more effective to wait and hold the demonstration next winter. "The winter is the time when most people are willing to focus attention on the problem," he said.

The appeals court ruling would allow sleeping in the parks only for the planned CCNV demonstration. A general Park Service regulation against sleeping overnight on federal grounds still stands, Assistant U.S. Attorney Royce Lamberth said yesterday.

Lamberth said the government intends to seek a 30-day stay of the appeals court order to allow the solicitor general to decide whether to take the case to the Supreme Court. It had been the government's position that the demonstrators could construct the tents at the two sites and even stay overnight, but could not actually sleep in them because this would be a violation of Park Service regulations.

Lamberth, chief of the U.S. Attorneys Office Civil Division, said that if the CCNV decides against holding the demonstration, the government will seek to have the appeals decision vacated, which would mean that yesterday's ruling would have no bearing on future attempts by the group to hold the same kind of demonstration.

Snyder and his attorneys from the American Civil Liberties Union and the Institute for Public Representation hailed the appeals court decision as a victory for First Amendment rights. The court ruled that in this case, the right of the homeless to sleep in the park is a form of expression protected under the First Amendment right to free speech.

"As applied to CCNV's proposed demonstration, the government's ban will clearly affect expression: There can be no doubt that the sleeping proposed by the CCNV is carefully designed to express the demonstrators' message that homeless persons have nowhere else to go," wrote Judge Abner J. Mikva in an opinion in which Chief Judge Spottswood W. Robinson III and Judges Patricia M. Wald, J. Skelly Wright, Harry T. Edwards and Ruth Bader Ginsburg joined.

The judges ruled that the act of sleeping, in this case, must be considered a symbolic form of free speech, like marching or picketing.

But in dissenting opinions, Judges Malcolm Richard Wilkey and Antonin Scalia said that the First Amendment right covers only the written and spoken word and some more traditional forms of protest such as marching and picketing.

Wilkey said in his opinion that he believes the majority ruling issued yesterday will give rise to widespread sleeping in the parks. Judges Edward A. Tamm, George E. MacKinnon and Robert H. Bork also dissented.