Vitaly Yurchenko, a high-level KGB defector who says he wants to return to the Soviet Union, emerged from the State Department last night with hands clenched above his head in a victory sign and shouted, "Yes, home!" after an hour of questioning and medical observation to determine whether he was leaving voluntarily.

He was expected to depart immediately for Moscow.

"The United States government has decided that Mr. Yurchenko's decision to return to the Soviet Union was made of his own free will and that he is now free to leave the United States," State Department spokesman Charles E. Redman told reporters afterwards.

But the meeting, which ended the negotiations between U.S. and Soviet officials over Yurchenko's departure, offered no new clues as to why the 49-year-old Soviet spymaster was leaving after three months of intensive debriefing by Central Intelligence Agency and Federal Bureau of Investigation officials who still maintained he provided important and verifiable information. State Department spokesmen and a senior administration official cited "personal" reasons and a "change of heart" to explain why Yurchenko walked away from his CIA protectors on Saturday while having dinner at a restaurant "a few hundred yards from the Soviet compound" just above Georgetown in Northwest Washington.

Senior intelligence sources said Yurchenko was romantically involved with the wife of a Soviet diplomat in Canada and may have had expectations that the woman would join him in a new life in the United States. But during what was described by one source as a secret trip to Canada taken by Yurchenko shortly after his defection, the Soviet may have been spurned by the woman.

"Love motivates a great deal and that may be part of his motivation," said Sen. Patrick J. Leahy (D-Vt.), vice chairman of the Senate Select Committee on Intelligence. "But I would think that a man of this caliber, a man so involved in the KGB, would still have a lot more than just a ruined love affair to determine what he was going to do."

A CIA official also pointed out that Yurchenko complained during a Monday news conference at the Soviet Embassy that the members of his CIA debriefing team did not speak Russian and he was forced to speak English for three months. He also complained that he might be entangled in legal proceedings after he was identified in news reports as the source for the CIA's confirmation that KGB agents a decade ago chloroformed and killed Nicholas G. Shadrin, a Russian defector working for the CIA as a double agent, in Vienna.

Yurchenko also alleged that he had been drugged during his CIA debriefing but one Senate source said that the only drug administered to the defector was medication for an ulcer.

Another Soviet defector yesterday criticized the CIA's handling and support of defectors. E. Alexandra Costa, the only person to defect from the Soviet Embassy in Washington in four decades, said in an interview that she knew Yurchenko -- who was then posted in Washington -- from 1975 to the day of her defection in August 1977.

Costa -- a name she assumed after defection -- described Yurchenko as the internal security officer for the 700-member Soviet Embassy staff. "My husband [a first secretary] pointed him out to me and told me he was a very dangerous man."

She recalled that her husband had said to her, "Don't say anything to him." Costa described Yurchenko's job as making sure that embassy employes had "correct attitudes" and to instill in them the firm belief that Soviet officials had penetrated the CIA and the FBI and would discover any defection attempts.

She said Yurchenko was not involved in any intelligence-gathering during his years in Washington.

Sens. David F. Durenberger (R-Minn.), the chairman, and Leahy, the vice chairman of the Senate intelligence committee, smarting over not being informed by the CIA of breaking developments in the Yurchenko case, were briefed yesterday afternoon by CIA officials.

Leahy told reporters that CIA officials believe Yurchenko was a genuine defector who became emotionally upset. But Leahy said he and other members of the committee believe that Yurchenko may have been part of an elaborate "sting" to embarrass U.S. intelligence on the eve of the Geneva superpower summit and after an embarrassing string of Soviet defections from Athens and London earlier this year.

"I still find it incredible that a senior KGB official would think that he could defect, then redefect, and the dacha would still be there at the Black Sea. He'd be under it, not on it," Leahy said.

Leahy said a number of senators on the intelligence committee had expressed "concern and misgivings all along" about Yurchenko, but that the CIA had maintained confidence in him.

"They had gone through such careful procedures in questioning, double-checking, polygraphs and all, that they were sure he was for real," Leahy said. "I would suspect they still feel he was for real."

One senior intelligence official said yesterday that he believed Yurchenko was not a Soviet "plant," but rather was a genuine defector who had undergone a change of heart.

Asked how Yurchenko had managed to get away, the senior intelligence official said Yurchenko was "a free man" and had been granted asylum and, therefore, could go wherever he liked. He said the CIA had done everything it could to make Yurchenko happy during the three months he had been undergoing debriefing since he walked into the U.S. Embassy in Rome on Aug. 1 and negotiated his defection.

The senior intelligence official also said the matter is still unresolved and that he might change his assessment over the next few days.

Without addressing the authenticity of Yurchenko's defection, Secretary of State George P. Shultz, who is in Moscow for a series of presummit meetings, added his voice to the denunciation of Yurchenko's allegation that he was kidnaped, drugged and held against his will by the CIA.

"The charges he has made are totally false," Shultz told reporters.

Meanwhile, in rural Virginia, reporters and camera crews swarmed over the remote subdivision identified by Yurchenko as the location of the safe house where he spent three months "in captivity." Based on interviews with neighbors, the residence believed to have served as the safe house is owned by a Fairfax County man who is listed in a 1983 membership directory of the Association of Former Intelligence Officers.

Sen. Malcolm Wallop (R-Wyo.), the leading advocate for a counterintelligence agency separate from the CIA, said yesterday he believed Yurchenko was a false defector from the beginning.

"I would be stunned if there were any other explanation," he said. "He's been in the KGB all his professional life. He knows what they do to traitors. Do you think . . . they'd take him back and let him spend the rest of his life with his wife and kid?"

Added Wallop, "He's going to get a medal, not a trial."