U.S. Trade Representative William E. Brock, in what the administration is billing as a major breakthrough in the auto import impasse, will fly to Japan today in a new attempt to resolve the auto crisis before Prime Minister Zenko Suzuki visits Washington next week.

A high-ranking administration official said Brock is making the trip in response to a request Suzuki made over the weekend. Brock will discuss the administration's political dilemma on the auto question, rising sentiment in Congress to restrict Japanese car sales here to help the U.S. industry retool and become more competitive, and other trade problems. Brock will not negotiate any agreement. To maintain its free-trade posture, the Reagan administration will not suggest any import limits, but will welcome any help the Japanese want to give, the administration source said.

Brock is expected to confer with Suzuki, the Japanese foreign minister and the minister of the Ministry of International Trade and Industry, another official said. The Japanese urgently want to resolve the issue before Suzuki's visit, but U.S. officials aren't sure exactly when the Japanese will announce any decision, the official said. Brock wouldn't go to Tokyo if the Japanese "weren't very sincere" in wanting to end the problem, the official said.

Not only is the auto question a delicate political issue in Japan where different factions of government and the automakers are bickering, but Brock must explain the difficulty of Reagan possibly vetoing popular but protectionist import legislation while trying to get his economic recovery program through Congress.

Brock will explain that Congress intends to pass legislation limiting Japanese exports to 1.6 million units a year, about 300,000 less than shipped here last year, and that the only concession the administration can make in return for voluntary import restrictions by the Japanese is a promise to oppose the legislation, the official said.

The Japanese automakers, who last week rebuffed direct appeals by their government for export restraint, have said they will hold exports to 1.82 million cars, the number they sold here last year. But Brock is expected to tell the government officials that such a cutback -- or one for less than three years -- would receive a negative reaction from Congress and would build momentum for passing stiff quotas, the official said.

The Japanese requested for several weeks a high-ranking delegation to discuss the auto question, the official said. However, Brock only agreed to the visit this weekend when Suzuki said he would discuss opening trade in other areas such as agriculture, semi-conductors, leather and services and reducing nontariff barriers, the official said.

The format for the talks was unclear yesterday. The official said he wasn't sure exactly what the Japanese wanted to ask Brock and whether he would be used as a sounding board to come up with voluntary import limits that might be acceptable to Congress.

In addition to discussing the increasingly protectionist mood in Congress, Brock will say that the auto industry management and labor are willing to make great concessions to help themselves. The Japanese automakers, angered that they are being asked to sacrifice for the sake of the U.S. auto industry, have urged that Detroit contribute more.

However, the official noted that the United Auto Workers union is facing elections this spring and it will be difficult for a candidate to run on a platform of cutting wages and benefits to help the industry as a whole.