By Edward D. Sargent
Washington Post Staff Writer

A U.S. Park Police officer was assaulted and slightly injured yesterday morning when he tried to arrest several persons who were sleeping in Lafayette Square, across the street from the White House, Park Police officials said.

Officer David Haynes, who was trying to enforce a controversial regulation that prohibits sleeping in the park, was knocked to the ground during the 6 a.m. altercation, officials said. Haynes jammed his thumb during the scuffle, they said.

Another officer reported to the scene and helped Haynes subdue and arrest seven persons. Three of them were charged with assaulting a federal officer, and all were charged with camping in the park, officials said. In addition, a woman who was naked from the waist down was arrested and charged with indecent exposure, officials said.

It was not certain whether any of those arrested were protesting at the time, police said.

The Supreme Court is considering the question of whether demonstrators seeking to dramatize the plight of homeless Americans have the constitutional right to express themselves by sleeping overnight at Lafayette Square and on the Mall.

Former interior secretary James G. Watt issued a ban in 1982 against sleep-ins in certain national parks after demonstrators erected a tent city dubbed "Reaganville" at Lafayette Square. The protest, held on Thanksgiving 1981 by the Community for Creative Non-Violence (CCNV), was in protest of Reagan-administration reductions in aid programs.

In March 1983, the U.S. Court of Appeals upheld CCNV's right to sleep in a 6-to-5 ruling that the government appealed to the Supreme Court in William P. Clark, Secretary of the Interior v. The Community for Creative Non Violence.

Lawyers for the American Civil Liberties Union, who are representing the CCNV, have argued that the right of CCNV's Thanksgiving Day demonstrators outweighed the government's interest in preserving tranquility in the park.

In arguments before the Supreme Court, Paul M. Bator, the Justice Department's deputy solicitor general said the government's only interest in curbing the CCNV protest was to "save the parks from intense . . . and continuous occupation" by protesters whose actions would interfere with the rights of others to enjoy the park.