It was the first time an official of the Soviet Union had testified before a House committee, a symbol, Vitaliy Churkin said, of his government's willingness to be "very forthcoming" in responding to the public relations fallout from the Chernobyl nuclear accident.

But the appearance of Churkin, a second secretary of the Soviet Embassy here, turned into a clash of political philosophies that revealed few new details of what is being called the world's worst nuclear disaster.

For more than an hour, the well-tailored diplomat, displaying an array of English slang and the Gorbachev emphasis on image, parried with members of the House energy, conservation and power subcommittee. He fended off the political barbs of one congressman as "mumbo jumbo" and advised the panel not to use such a "commanding tone" if it hoped to elicit cooperation from Moscow.

When subcommittee Chairman Edward J. Markey (D-Mass.) demanded to know why the Soviet government has failed to inform its own people of the accident, Churkin replied that "the citizens who were affected by the accident are very well taken care of, and if they have any medical problems they will not even have medical bills to pay."

Asked whether American farmers should prepare for increased Soviet purchases of grain because of radioactive contamination in the Ukraine, the breadbasket of Russia, Churkin noted dryly, "I understand this question was not based entirely on humanitarian grounds."

"We are in a capitalist country right now," Markey shot back.

"I realize that very much," said the Russian.

The sometimes spirited repartee was reminiscent of past Hill hearings, with members of Congress grilling the witness and the witness artfully dodging the hard questions.

At one point, Rep. Norman F. Lent (R-N.Y.), noting that the subcommittee was addressing Churkin as it would a U.S. official, conceded that "perhaps we've been unfair" in demanding detailed scientific information.

"I'm glad you realize that," the diplomat replied, seemingly undaunted.

Churkin, who appeared after the Markey staff extended an invitation to the embassy, noted the "unique experience" of a Soviet official testifying before a House panel. But he quickly established limits by reminding questioners that he was an embassy employe, not a nuclear scientist.

Asked repeatedly by panel members about the cause of the Chernobyl accident, Churkin met the questions with a question of his own: "Can you tell me in certain terms why the Challenger accident happened?

"I'm not trying to be polemical, but it's a technical matter."

But with the session under the lights of television crews, the politicians took the opportunity to contrast Soviet secrecy with the American way of facing catastrophes.

"We deal with our problems in the open," said Rep. Ron Wyden (D-Ore.). "That's what we'd like in the Soviet Union."

But the Russian turned back the criticism, reminding panel members of just how far they could go.

"Isn't it true, Mr. Churkin, in reality that you should not have been celebrating May Day but radioing 'mayday' the international distress call to your citizens and neighbors with regard to the danger?" Markey asked.

"Mr. Chairman," Churkin replied, "I believe it would not be correct on my part to accept any advice coming from you, with all due respect, on what we should have or should not have done in our country . . . . "

He bristled when panel members suggested that Soviet reports of two fatalities and 197 casualties understated the toll at Chernobyl, calling such accusations "a little offensive" and "an unusual psychological reaction."

"I categorically reject any suggestion of some untruths in our statements," he said.

After his Hill appearance, Churkin sat for an interview on the "MacNeil/Lehrer NewsHour." Asked if the Soviet government had approved of his testimony, he replied, "I don't think we asked. We're very courageous fellows here."