Washington Ballet Artistic Director Mary Day, Resident Choreographer Choo San Goh, Executive Director Elvi Moore and outgoing President Jean Sisco announced at a ballet champagne reception at the Watergate Hotel Tuesday that the company had received an Exxon corporation $50,000 grant to commission a new ballet by Judith Jamison . . .

Lady Bird Johnson was in town Tuesday night drumming up support for the National Wildflower Research Center in Austin, Tex. A benefit for the center, which was founded by Lady Bird, will be held on Sept. 29 at the Middleburg home of former governor Averell and Pamela Harriman. She was at a reception at the Kalorama home of Penne and Fritz-Alan Korth to meet with a group of Washingtonians who have agreed to be on the benefit's star-studded committee, including Sen. Lloyd Bentsen Jr., Rep. Jake Pickle, Treasury Secretary James Baker III and his wife Susan, Labor Secretary Bill Brock and his wife Laura and Motion Picture Association head Jack Valenti . . .

The Japanese dance troupe Sankai Juku has canceled its seven-city U.S. tour after one of its members plummeted six stories to his death Tuesday before a horrified crowd in Seattle on the group's first American tour. The group had been scheduled to perform here at the Warner Theatre in November . . .

Since Rock Hudson is still too ill to make an appearance at the Sept. 19 gala in Los Angeles to benefit AIDS research, New York Daily News columnist Liz Smith says that Elizabeth Taylor is setting up a special telephone hookup to Hudson's bedside so he can speak to the assembled crowd . . .

The National District Attorneys Association will present Attorney General Edwin Meese with a life achievement award at a black-tie dinner Saturday at the J.W. Marriott Hotel, commemorating "his dedication to law enforcement issues" . . .