U.S. and Japanese negotiators trying to rewrite a complex civil aviation agreement between the two countries said today that lack of progress had forced them to schedule at least three new rounds of talks.

During five days of meetings in Tokyo this week, the two sides failed to resolve the immediate problem facing them, a new Japanese cargo carrier's request to fly into the United States starting April 1.

The U.S. chief negotiator, Deputy Assistant Secretary of State Franklin Willis, indicated today the two sides remain far apart. "We are continuing to examine the whole set of issues," he told a press conference.

The apparent stalemate added a new dimension to trade tensions between the two countries, which have been intensified by the United States' $36.8 billion trade deficit with Japan last year.

During the negotiations, the United States has aired many of the same complaints about doing business in Japan that have dominated separate talks aimed at increasing sales of U.S. telecommunications equipment in Japan.

The round of aviation discussions this week was the third in a 15-month timetable to revise the 33-year-old civil aviation accord, which governs passenger and cargo flights on the profitable trans-Pacific route.

Negotiators had originally planned to finish the job at a fourth and final round to be held before the end of September. Now, however, they have decided to hold at least three more, in May, June and July.

The agreement is a traditional point of discord between Washington and Tokyo. It was signed in 1952, the year the United States ended its military occupation here, and Japan has complained that the document reflected its status at the time as a defeated nation.

The United States contends, however, that the agreement is balanced.

Currently, five U.S. carriers and one Japanese -- Japan Air Lines, the country's sole overseas operator -- fly the Pacific route. American planes have rights to land in three Japanese cities, while the Japanese can call at nine U.S. cities.

In the final accord, both sides want to increase their airlines' flexibility in selecting routing, destinations after stops in the foreign country and seat capacity.

In the short term, however, the question is U.S. landing rights for the new carrier, Nippon Cargo Airlines (NCA), starting on April 1.

With five U.S. airlines operating here already, the Japanese say, it is only fair that the United States grant NCA's request.

But U.S. trade negotiators point out that NCA is owned by major Japanese shipping companies and freight forwarders. They contend that, as a result, it could unfairly take business from American cargo carriers.

"The people who forward freight own the line. So guess where all the freight is going to go," said a U.S. trade official here.

NCA already has purchased aircraft. Its managers have suggested publicly that they will press the Japanese government to retaliate if the United States does not give the airline the go-ahead for an April 1 start-up.

Willis said the United States would not insist on holding up an accord on NCA until all other aviation issues were settled. But at the same time, he hinted that the two were linked in the U.S. mind.

U.S. carriers wanting to enter Japan have had to "strike a bargain," Willis said in response to a Japanese reporter's question today. "So we're only asking the same," he said. Willis said a major U.S. objective in the talks was to reduce "a web of regulations" that he said is hampering U.S. airlines' ability to compete in Japan.

Currently, he said, U.S. carriers are flying only about 50 of 300 one-way charters they are allowed each year. He blamed it on Japanese regulations. "It's simple, and that's the only thing you can point to," he said.