The Japanese government today spelled out three conditions the United States must meet if it hopes to negotiate a voluntary limit on imports of Japan's steel products.

It was the first time the government has given any hint of what it expects in return for inducing Japanese companies companies to cut back sales of steel to the U.S., source of the nation's most critical current trade dispute.

As spelled out in press reports and confirmed by an official of the Ministry of International Trade and Industry, the conditions are:

Assurances that Japanese steel companies by jointly curbing steel exports, would not be vulnerable to anti-trust litigation in American courts.

A commitment by the Carter administartion that the U.S. Steel corp, would be induced to drop its pending complaint of steel "sumping" against Japanese companies.

A U.S. promise to force similiar restrictions on imports from countries of the European Economic Community.

Japanese officials said that they had not arrive at an estimate of how much steel tonnage exports would be reduced if those conditions are met.

Yesterday, the Treasury Department tentatively hald that five Japanese companies illegally are dumping carbon steel products in the U.S. at prices 24 per cent below their cost of production. Dumping is classically defined as selling products in expert markets for less than their price in home markets. The prelimary ruling will be reviewed before a final report is handed down by the department in three months.

If the final opinion affirms the preliminary holding, the case would be referred to the International Trade Commission, which would make a recommendation on the case to President Carter.

It is unlikely that yesterday's holding will be affirmed in light of ongoing administration work on a relief packages for the domestic steel industry.

A prominent economic journal, Nihon Keizai reported today the U.S. had proposed that Japan reduce stell exports from 7.6 million tons in 1976 to between 5 and 5.5 million tons a year. American officials here disputed the reports and said no specific level of exports had been suggested.

The initial American reaction today was a measure of optimism that specifics of a steel settlement were in the open, tempered with doubt that all three conditions could be met.

One official said the administration could not legally force U.S. Steel to abandon its formal dumping complaint.

But another condition - the one requiring similiar in steel imports from EEC countries - would be a "normal" requirement fo any settlement, he said.STA pledge to exempt the Japanese companies from antitrust action raises problems that might bot be easily resolved by the U.S. Government.

Past voluntary agreements to restrict Japan's exports of steel were attacked in a suit brought by consumer groups in 1972. Although a district court judge held the agreements did not violate antitrust law, those agreements were abandoned before appeals were concluded.

The Japanese insist that they do not want to go through another siege of antitrust lawsuits if they volutarily agree to cut back on their exports. Unless imminity is promised, one senior official of the Trade Ministry said, it would be "dangerous" for Japanese companies to make jointly-conceived reductions.

Sudden, sharply lay offs workers in American mills have put the steel issue at the top of the list of trade querells between the two countries. Pressures are rising in Congress to restrict imports from Japan.

The Japanese contend that superior technology and good management permit their companies to sell stell products in the U.S. at desirable prices.

In August, a senior Japanese trade official, Naohiro Amaya, went to Washington to discuss a voluntary restraint on Japanese sales.

Since then, U.S. Ambassador Mike Mansfield has endorsed the concept of imposing on steel and orderly marketing agreement similiar to the one which reduced exports of Japanese television sets to the U.S.