It appears that Mark Thatcher, son of British Prime Minister Margaret Thatcher, won't be shooed away by his new Texas neighbors after all. The board of directors of the high-rise condominium where Thatcher lives rejected the suggestion of five apartment owners that he be forced to move because of the target he presents for terrorist attacks. In a notice sent to all units, the board said Thatcher's neighbors have no legal right to seek his ouster and said he is free to stay. Thatcher was forced to leave another Dallas apartment last month when his landlords said they couldn't protect him from terrorist threats.

News of the neighbors' request prompted former senator John Tower to say the fearful residents made Texans look like "a bunch of yellow-bellies," which the tabloid London Daily Mail certainly believed to be true. Its story began, "Mark Thatcher is being hounded from his home for the second time by terrified Texans.

Actor Martin Sheen, activist Rev. Daniel Berrigan and 17 other people were arrested yesterday in New York City as they blocked the doors to a defense research firm.

Charged with trespassing, the protesters were among 40 members of the Kairos Community, an antiwar Christian group that picketed the Riverside Research Institute, which they believe is conducting research into nuclear weapons. Riverside's security officer, Bill Jackson, denied that the company researches weapons but said it does hold Defense Department contracts.

A group of five women is planning to picnic topless today in a Rochester, N.Y., park to protest a state law forbidding women -- but not men -- from going bare-chested in public.

Protest organizer Ramona Santorelli stressed, "It's not a trivial issue. Just try to tell any man on a hot summer day that he can't take his shirt off."

Deputy Police Chief Terrence Rickard said the women will be arrested only if people complain. Santorelli says her group is looking to get arrested and the women will go so far as to call the police themselves. Those arrested could face a maximum penalty of 15 days in jail or a $250 fine . . .

Conductor and composer Leonard Bernstein and writer James Baldwin were both made Commanders of the Legion of Honor, one of France's highest awards, by President Franc,ois Mitterrand Thursday. Mitterrand saluted both men for "creating a fundamental solidarity between men which we would be poorer without."

Aside from such accomplishments as Bernstein's award-winning musical "West Side Story" and "Mass," composed in memory of President Kennedy, Mitterrand thanked Bernstein for always being a friend to his country. He saluted Baldwin, best known for such books as "Another Country," "The Fire Next Time" and "Giovanni's Room," as a writer and "defender of human rights" . . .

The St. Louis Zoo said yesterday it will pay tribute to the late Marlin Perkins by constructing a plaza and theater in his honor. Robert Hyland, president of the Zoo Commission, said the zoo has received a gift of $100,000 from an anonymous donor to be used to establish a fund for the construction of the Marlin Perkins Conservation Theatre. "The message for the Conservation Theatre will focus on the survival of endangered species," said Charles Hoessle, zoo director. Hyland also said the zoo commission will honor Perkins by constructing the Marlin Perkins Plaza adjacent to the Big Cat Country Railroad Station. Perkins, 81, died from cancer last Saturday in his home in Clayton. He was director of the St. Louis Zoo from 1962 to 1970, and was named director emeritus upon retirement.