Deputy assistant to the president and director of presidential scheduling Frederick Ryan got engaged Wednesday to Genny McSweeney . . .

Zenani Mandela Dlamini, daughter of South African resistance leader Nelson Mandela, will accept a check for approximately $6,500 from Sen. Howard Metzenbaum today at the Russell Senate Office Building, according to Barbara Harmel of the Center for Developmental Policy. Thirteen senators each donated $500. The money will be used to help rebuild Dlamini's mother's home and clinic, which were recently firebombed. . .

Bandleader Xavier Cugat, 85, may take girlfriend Yvonne Martinez for his sixth wife, according to Cugat's fourth wife, Abbe Lane. . .

Congressman Tom Bevill is in satisfactory condition after undergoing quintuple coronary bypass surgery Wednesday night at University Hospitals in Birmingham, Ala., a hospital spokesman said. Bevill, 64, a 10-term Democrat, may remain hospitalized up to 10 days . . .

Rock star Mick Jagger reportedly promised to marry his longtime girlfriend, model Jerry Hall, if she gave birth to a son. Hall kept her part of the bargain, delivering a healthy boy on Wednesday. The New York Daily News quoted a source close to Jagger as saying the singer will probably keep his word. The wedding would take place in Jagger's cha teau in France before Thanksgiving, the newspaper said. . .

Former president Jimmy Carter is so eagerly looking forward to the White House staff reunion in Plains, Ga., this weekend that he went out and mowed his field so the 225 visitors could play softball. . .

Dr. Dennis Lincoln of Edinburgh University said yesterday that there are 1 billion acts of sexual intercourse per year in Britain alone. Speaking to the British Association for the Advancement of Science, Lincoln said passion in Britain is not unusually high, but merely reflects the fact that humans are the most highly sexed mammals on Earth. "I believe the human animal is about 10,000 times more sexually active than the rabbit," said Lincoln, who heads a reproductive biology unit. But he added, "Don't ask me how I calculate these figures because the Chancellor of the Exchequer might want to put a tax on it.". . .