WASHINGTON (AP) — Police are starting a search of vacant buildings in the nation's capital, looking for clues in the disappearance of former federal intern Chandra Levy, who had ties to a member of Congress.

Meantime, negotiations are under way to set conditions under which Rep. Gary Condit, D-Calif., would submit to a lie detector test in the case. Condit, who police say is not a suspect in Levy's disappearance, told authorities last week that he had a romantic relationship with the 24-year-old woman, police sources say.

"We have to explore the possibility that she may be dead and we're looking for the remains," said Terrance Gainer, the city's No. 2 police official. "So we're looking at about one-seventh of the District of Columbia right now, at abandoned buildings.

"Our officers begin walking through those buildings today and we may use cadaver dogs if it's necessary," Gainer said on CBS' "The Early Show."

Gainer said investigators are still working on four theories in Levy's disappearance: that she was a victim of foul play, committed suicide, walked away voluntarily or is wandering around not knowing who she is.

The assistant chief said he talked Wednesday with Condit's lawyer, Abbe Lowell, about having the congressman take a lie detector test. "The congressman's attorney has suggested we can get to a polygraph" test, Gainer said.

The Washington Post and CNN, citing police sources, reported police have asked three other men to take polygraph tests. One said he occasionally socialized with Levy, but the connection of the other two to Levy was not immediately clear.

Several items taken from Condit's apartment during a search that ended at 3 a.m. Wednesday were being turned over to the FBI crime lab in Quantico, Va., said Sgt. Joe Gentile, a police spokesman.

Condit voluntarily allowed the search of his home to show his cooperation in the search for Levy, a constituent from Modesto, Calif., whom he has described publicly as a good friend.

The Post reported in Thursday's editions that FBI agents have interviewed a Pentecostal minister who described an affair between his then-18-year-old daughter and Condit.

The minister, Otis Thomas, was quoted by the Post as saying that Condit had told his daughter never to speak of the relationship. Thomas said his daughter is afraid to talk with the FBI and has gone into hiding. Thomas, whose church is in Modesto, Calif., did gardening work at the Levy home in Modesto, the Post said.

Thomas told the Post that his daughter met Condit at a political rally and ended the relationship about seven years ago.

Asked about that report, Gainer would say only that "the names and stories aren't unfamiliar to us."

Marina Ein, a spokeswoman for Condit, said the Post report was "discountable — there's no confirmation from the principal," referring to the daughter.

Asked if she was denying the congressman had an affair with the woman, Ein said: "We're not going to get in the territory of accounting for each and every one of the tabloid cases that are presented."

Telephone messages left with spokesmen for the Levys late Wednesday night were not returned. Attempts were unsuccessful to locate Thomas in Modesto, or reach him by telephone at a number of possible home and church numbers.

Levy was last seen canceling her membership at a Washington health club. Her internship with the federal Bureau of Prisons had just ended, and she was planning to return home for graduation ceremonies at the University of Southern California.

Police searched her apartment and found nothing missing but her keys. Her bags were packed.

Condit, 53 and married, told police last week that he had an affair with Levy, according to a source familiar with the investigation. His staff had claimed for weeks that they were just goods friends.

The disappearance still is being treated as a missing-person case and police have said repeatedly that Condit is not a suspect.

While police looked for new information, the FBI and the U.S. attorney's office again questioned flight attendant Anne Marie Smith. She has contended Condit asked her to sign a statement denying a 10-month affair she says they had.

Authorities declined comment on the questioning.

Smith said on Fox News Channel that investigators indicated she had provided them with new information during the six hours she met with them. She would not disclose what she told them, but said she would meet with them again Thursday.

Smith said she and Condit never talked about Levy. She said she last spoke to Condit 2« weeks ago and that he again urged her to sign the statement.

Condit has not commented on any relationship with Smith, but in a statement last week said he never asked anyone to lie.