The case of the Soviet defector who disappeared in Austria 18 months ago on a counterintelligence mission for the FBI has been the subject of numerous formal and informal Soviet-American contacts, including one direct exchange between President Ford and Soviet leader Leonid I. Brezhnev.

None of these contacts produced confirmation from teh Soviets that they knew the whereabouts of Nikolai F. Artamonov alias Nicholas G. Shadrin. Shadrin's wife, a McLean, Va., dentist, believes her husband was kidnapped by Soviet KGB (secret police) agents and taken to the USSR.

Last Dec. 3 Ford sent a letter to Brezhnev asking him to take a personal interest in the case to find out where Shadrin was.

Shadrin disappeared in Vienna on Dec. 20, 1975, when he was supposed to be meeting KGB agents in a prearranged contact. At that time Shadrin had been acting as a double agent for the FBI for nine years. He defected in 1959.

Ford also assured Brezhnev that the U.S. government would not publicly comment on the case and would urge Mrs. Shadrin and her husband - if he were returned - not to comment on it. Ford indicated he would do all in his power to help Mrs. Shadrin to reunite with her husband.

On Christmas Eve Brezhnev's answer was conveyed in Washington orally by a Soviet diplomat. The Soviet leader said he had read the entire file of the case. He confirmed that the missing man had been a Soviet citizen and a naval officer. He contended that the man had approached representatives of the Soviet Union in Washington in 1966, asking to be allowed to return home.

(By Mrs. Shadrin's account, her husband was approached by KGB agents in 1966 and asked to spy for his orgiginal homeland. He reported this to the FBI, she says and the bureau asked Shadrin to cooperate, acting as a double agent - a "Flycatcher," in the jargon of the trade. Artamonov/Shadrin agreed to do so, his wife says.)

Brezhinev's message to Ford said Artamonov Shardin told Soviet representatives in 1966 that he had been forced to work for U.S. intelligence, and that this disturbed him, and he wanted to return hom and to see his wife and child. (He had left a wife at the time of his defection: she had a child by a previous marriage, according to Mrs. Shadrin.)

Brezhnev said further that the Soviet Union had agreed to Artamonov Shardrin's request for a meeting in Vienna in December, 1975. He repeated his desire to return home at that time. Brezhnev said, but then failed to appear for a second meeting two days after.

Mrs. Shadrin and the U.S. government believe that Artamonov-Shadrin was kidnapped on his way to the second meeting. Mrs. Shadrin and her lawyer, Richard D. Copaken,accuse the Ford administrationo f trying to meekly to retrieve Artmonov/Shadrin, and of bungling many potential opportunities to help.

President and past-government officials said yesterday thischarge was unfair. Several pointed to Ford's personal and forceful letter to Brezhnev, which Copaken himself has described to The Washington Post.

Copaken, the lawyer, accused former Secretary of State Henry A. Kissinger of willful obstruction of efforts to help Artamonov/Shadrin. Through a spokesman, Kissinger replied yesterday that this version was "an irresponsible distortion of the facts."

"There are few cases in which the United States has so exerted itself as on this one," Kissinger said.

White House press secretary Jody Powell said yesterday that Mrs. Shadrin "has and continues to have the active support of this administration."

Copaken contends that he opened a potentially fruitful channel to the Soviets through Wolfgang Vogel, an East Berlin lawyer who arranged the 1960s' swap of Francis Gary Powers, the U-2 pilot shot down by the Soviets, for Col. Rudolph Abel, allegedly a Soviet master spy who was a U.S. prisoner at the time.

Vogel conveyed the impression that a trade might be made involving Artamonov/Shadrin and Guenther and Christel Guilliaume. East German agents long sentences in West Germany. The discovery that Guillaume, an intimate adviser of former West German Chancellor Willy Brandt, was a spy helped pushed Brandt into retirement in 1974.

Vogel also told Copaken, the lawyer said, that it had required a telephone conversation between Brezhnev and the leader of East Germany. Enrich Honneker, before Vogel was authorized to discuss a possible trade with the American lawyer. Copaken says he asked Vogel if this was a sign that Artamonov/Shadrin was alive and in Soviet hands. Vogel confirmed that it was such a sign, according to Copaken.

(Like Brezhnev's, all official. Soviet statements on the case have denied knowledge of Artamonov/Shadrin's whereabouts. Several sources in the American intelligence community have speculated that his return to the Soviet Union may have been voluntary - that he was a Soviet agent all along. But other government officials heatedly dispute that view.)

Copaken's relations with the East German Vogel collapse last year after U.S. officials violated the terms of his understandings with Vogel, Copaken says.

Vogel demanded that no information that passed privately between him and Copaken be repeated in formal communications between the U.S. and Soviet governments. However, Copaken charges. Kissinger and his associate, William Hyland, both used official channels to repeat information that came to him from Vogel. Copaken says this may have been deliberate.

It was this that Kissinger described as an "irresponsible distortion" yesterday.

This year the Carter administration asked the West German government to press Vogel to reopen contact with Copaken, he says. Vogel agreed and in two meetings this year reiterated interest in a trade involving the Guillaumes or Jorge Montes, a Chilean Communist in prison in Chile. These proposals have not borne fruit - because of government bungling or indifference, according to Copaken and Mrs. Shadrin - and Vogel has again broken off relations.

Mrs. Shadrin suggested in an ABC-television interview yesterday, that President Carter could discuss the possibility of a trade involving the Guillaumes with Chancellor Helmut Schmidt during his visit to Washington. She pleaded with Carter to help her husband.

"He's of no use to the United States any more," she told The Post, but she said a President concerned about human rights should try to help her husband for "humanitarian reasons."

Mrs. Shadria, revealed that she is receiving her husband's salary from the Defense Intelligence Agency, his former-employer at the time of his disappearance. She gets biweekly check of about $668, she said.

According to her lawyer, the fact that the government is paying her this money more than 18 months after her husband's disappearance means it is officially believed that he is still alive.

Mrs. Shadrin also revealed the the Justice Department is contributing substantially to her legal cost. Copaken, a partner in the firm of Covington & Burling, has put hundreds of hours into the case and traveled repeatedly to Europe on her behalf.

Artamonow/Shadrin never told his wife he was a double agent for the FBI, she said. Instead, he thole her he was working secretly with some, Soviets who wanted to help the United States.