Another round of high-level negotiations between the United States and Japan over how to further open the Japanese market to foreign telecommunications equipment and services has failed to produce an agreement.

With an April 1 deadline drawing near, senior U.S. officials were set to fly back to Washington this weekend with new Japanese proposals presented in the talks, which have become the focus of mounting trade tension between the two countries.

"We have not reached . . . any definite conclusions. We have hope," U.S. delegation chief W. Allen Wallis, undersecretary of State for economic affairs, told reporters this afternoon after extensive talks in Tokyo. Japanese officials gave a similar assessment.

Japan delivered its proposals orally in a meeting this morning. It is expected to send Washington a written version next week, and no formal U.S. response is expected until then.

One U.S. official said the Japanese appeared to be giving ground on some issues, but that he would withhold judgment until seeing the final wording of Japanese regulations. Often, he said, "they are not written as we had thought they would be written."

In Washington, U.S. officials are depicting the negotiations as a barometer of Japan's good faith in correcting a trade imbalance that, by Japanese figures, gave the United States a $34 billion deficit with Japan last year.

During the talks, U.S. officials cited President Reagan's recent decision not to ask Japan to renew auto export quotas that will expire March 31 and noted he had expressed hope for "reciprocal market opening measures in the weeks and months ahead."

But compared with statements by other members of the Reagan administration in recent weeks, Wallis' tone was mild. He called for further talks before the April 1 deadline, though no dates were set.

An account of the negotiations by a senior U.S. official indicated the two sides remain stuck on many of the same highly technical points they have been debating for the past four months.

At issue is fine print in regulations being drafted by Japanese officials to govern the telecommunications service industry beginning April 1, the day on which Japan's sole phone company, the Nippon Telegraph and Telephone Public Corp., will go private and lose its monopoly.

The United States has alleged that the rules, as drafted, are either too vague or too restrictive.

They would give Japanese officials means to discriminate against foreign companies and perpetuate the virtual lockhold Japanese companies have established in the market, U.S. officials say.

The United States also is pushing for rights for U.S. companies and officials to give their views and take part in deliberations over future changes in policy in the field.

Japan contends it is working as fast as it can on the rules, that they will be nondiscriminatory and that it has given the United States unprecedented input in the process. The Japanese suggest that the real key to U.S. companies' success will be pricing and marketing aggressiveness in Japan.

Details of Japan's counterproposals were not available.

But a senior official in the Ministry of Posts and Telecommunications suggested Japan had given ground in major areas of concern to the United States.

"We have done our best," he said. Among them:

* Reporting requirements for large-scale computer networks will be simpler than originally proposed.

* Foreign companies wishing to sell equipment here will be allowed to submit their own test data to a certification agency, rather than the agency conducting its own tests.

* NTT and any other "common carrier" phone companies that come into being will not be allowed to "subsidize" their own computer network services with money earned elsewhere. That is meant to prevent unfair competition against smaller companies that are offering only computer services.

The talks this week were "sub-cabinet" level consultations conducted twice yearly between Japan and the United States.

The U.S. delegation included officials from the departments of State, Commerce, Agriculture, Treasury and Energy, the National Security Council and the Office of the U.S. Trade Representative. The next round of talks is expected to take place in September.

In addition to telecommunications, the two sides discussed sales of American electronics products, coal and oil, and drugs and medical equipment in Japan. Those talks, too, were inconclusive.