Japanese auto makers apparently have rebuffed a direct appeal from the government to restrain their exports and avoid a trade crisis with the United States.

After hours of meetings with Japan's trade minister today, auto executives publicly clung to their position that they would not reduce exports to the United States this year and appeared to be introducing new conditions that might make negotiations more difficult.

Executives of seven auto companies met separately with Rokusuke Tanaka, the minister of international trade and industry, who is trying to persuade them to cut back exports and satisfy President Reagan's appeal for Japan's "voluntary" restraint.

After the meetings, an official source at the ministry said he thought that "understanding has been improved" but conceded there had been no agreement.

In their public statements, the industry leaders insisted they would restrain exports only by holding them to last year's level of 1.82 million passenger cars. A bill pending in Congress would set a quota of 1.6 million cars a year for the next three years. It has been reported here, but never confirmed, that the trade ministry is urging a cutback to 1.7 million cars.

Takashi Ishihara, president of Nissan Motors and head of the nation's auto manufacturers' association, was described as adamantly opposed to a reduction as far as 1.7 million.

"In Mr. Ishihara's opinion, it is out of the question," a spokesman for the company said.

The public comments from both sides indicated a continuing stalemate, although there is widespread speculation that the auto companies will eventually move closer to the government's bargaining position.

But the manufacturers introduced a new feature today that may complicate the negotiations. As a condition for endorsing any restraint, they insisted on assurances that they would not become liable to antitrust suits in the United States.

They have said frequently that a voluntary restraint agreement would open them to suits by their American dealers, but this was the first time they have asked assurances of immunity as a condition for making a bargain.

They also insisted that the government make some moves to assure them that an export reduction agreement with the United States would not be followed by demands for similar restraint from Canada and the Common Market countries, some of which have vowed to demand treatment similar to that given exports to the United States.

It was not clear what form these assurances could take to satisfy Japan's auto companies, but a government representative is prepared to take up the antitrust issue in Washington next week, sources said.

The trade ministry hopes the auto industry here will go along with some restraint because it fears passage of the U.S. legislation that would fix an import quota for three years.

Tanaka, according to a ministry source, told the company executives today that under the current circumstances Japan must take some kind of action. He asked them in a general way to give him their cooperation, but the source said he did not mention a specific export figure and did not say how the government might enforce an industry-wide restraint.

The industry leaders also martialed a new set of statistics to back up their insistence that they should not cut back below 1.82 million cars this year.

They told Tanaka that American representatives project 9.5 million auto sales this year. If Japan merely kept its 21 percent share of the market, the level reached last year, Japanese manufacturers could sell about 2 million cars there. Therefore, they argued, by holding to 1.82 million cars they would in effect be restraining sales and sacrificing about 200,000 car sales in the U.S. market.

The government indicated today that a final decision will be made next Saturday in conferences that will include Prime Minister Zenko Suzuki, who is to leave the following week for a state visit to Washington.

Japan's ambassador to the United States, Yoshio Okawara, told reporters here today that unless Japan restrains its exports, the U.S. Congress is likely to pass the bill establishing a 1.6 million car quota.

He said the Japanese industry's offer to hold the line at last year's level would not be sufficient to prevent that legislation from passing.