Sen. Brock Adams has threatened to file a defamation suit against a Seattle surgeon who is rekindling allegations that Adams sexually assaulted the doctor's daughter in 1987.

The father, Dr. James Tupper, has written a letter to more than 140 political action committees urging them to cut off contributions to the first-term senator up for re-election in 1992.The Washington state Democrat has denied the allegations of sexual impropriety and is planning to run again.

PAC leaders representing environmentalists, labor, abortion rights and gay-rights activists said they support Adams and are ignoring Tupper's plea.

Adams said he and his lawyers were discussing filing a libel or defamation suit against Tupper.

Adams' announcement is the most recent turn in a drama that began shortly after his election to the Senate in 1986.

"Three months after becoming a U.S. senator, Brock Adams drugged and sexually assaulted our daughter Kari in his Washington, D.C., home," Tupper wrote in a letter to PACs obtained by The Associated Press on Monday.

"Nobody thinks Brock Adams can be re-elected - and he shouldn't . . . I am angry, as any concerned father would be, and want to do what I can to let people know what kind of person Brock Adams is," Tupper wrote.

Law enforcement officials in the District of Columbia said they found insufficient evidence to prosecute Adams but Tupper vowed at the time he would not let the issue rest if Adams sought re-election.

Kari Tupper, working on a doctorate at the University of Washington in Seattle, said the letter was her father's idea but she appreciates his efforts.