Rep. Gary Condit, D-Calif., has been subpoenaed to testify early next month before a grand jury investigating the disappearance of Chandra Levy, a source with knowledge of the investigation said Tuesday.

A Superior Court grand jury in Washington has been examining allegations that Condit and aides tried to prevent witnesses from cooperating with the Levy investigation.

The Washington Post reported the subpoena Tuesday, citing law enforcement sources. Last fall, the congressman disclosed that the grand jury had subpoenaed documents relating to the Levy case.

Condit has denied any involvement in Levy's disappearance. He and his aides also have denied attempting to silence anyone.

Levy, 24, of Modesto, Calif., disappeared without a trace in Washington nearly 11 months ago, shortly after she finished an internship at the U.S. Bureau of Prisons. Condit, 53 and married, reportedly told police that he and Levy were having an affair.

Police have no idea what happened to Levy, despite an extensive investigation that included scores of officers and recruits combing local parks and abandoned buildings. "There is no light at the end of the tunnel," Terrance Gainer, the deputy police chief, said.

Gainer said police do not consider Condit a suspect in the case.

Channing Phillips, a spokesman for the U.S. Attorney's office in Washington, would not confirm or deny the issuance of the subpoena. The investigation, he said, "is ongoing and active."

Condit aides in Washington and Modesto, Calif., referred calls to Mark Geragos, Condit's Los Angeles-based attorney. Geragos declined to comment Tuesday.

Federal law enforcement officials have said they were examining whether Condit and his aides may have obstructed the search for Levy by asking other women who alleged they had affairs with the congressman not to cooperate with police.

Defense lawyers said the focus of the grand jury investigation probably would be on obstruction of justice since police have no evidence of a crime and continue to classify the Levy investigation as a missing person case.

But, they said, prosecutors could ask Condit and other witnesses, sworn to testify truthfully, virtually anything once they take the stand in the secret proceedings.

Levy disappeared May 1, days before she was to return to California to receive her graduate degree from the University of Southern California.

Condit suffered his first loss in a 30-year political career when former aide and political protege Dennis Cardoza handily beat him in the March 5 Democratic primary in the 18th congressional district in California's San Joaquin Valley.

Condit has not said what he will do when his term ends at the end of the year.