TOKYO, SEPT. 17 -- Prime Minister Yasuhiro Nakasone will express Japan's "general willingness" to help the United States in the Persian Gulf when he meets with President Reagan Monday, but he will bring no firm proposals, Foreign Ministry officials said here today.

Japan, which imports close to two-thirds of its oil through the gulf, is under pressure to assist the United States and other western allies in protecting tankers from Iranian and Iraqi attack. Japan's constitution limits its military activities to self-defense, but officials here have suggested that Japan could help pay for the U.S. mine sweepers and tanker escorts.

"We cannot take any military action whatsoever, so the logical conclusion is that perhaps what we can do is financially contribute to the effort," said Foreign Ministry spokesman Yoshifumi Matsuda.

But Matsuda added that government deliberations on the issue are still too preliminary to allow Nakasone to make any commitments to Reagan. The two leaders are scheduled to meet in New York Monday in what is expected to be their last encounter before Nakasone's resignation at the end of October.

Officials here said they have received no official requests from Washington for assistance in the Persian Gulf. But many members of Congress, already disgruntled with Japan over trade issues, have said the nation should not receive a "free ride" in the gulf, and Ambassador Mike Mansfield on Monday urged Japan to contribute to the effort.

U.S. Navy ships have been escorting oil tankers through the gulf, where both Iran and Iraq have attacked noncombatant vessels during their war. U.S. helicopters also have swept the sea for mines.

Several European nations, after initial reluctance to join the United States, have dispatched mine-sweeping ships to the region.

Japan's constitution, imposed by the United States after World War II, renounces war and has been interpreted to limit Japanese forces to a strict self-defense role. Nakasone, who with U.S. support has stretched the definition of self-defense further than any previous prime minister, said last month that Japan could send mine sweepers to the gulf without violating the constitution.

But he said he would not send them "because there is a possibility that they would become involved" in combat.

As a result, Japan has been studying various indirect ways to contribute, including increasing its payments in support of U.S. forces in Japan. But Matsuda said no consensus has been reached.

"This is quite a delicate and very difficult issue to tackle, involving a huge amount of money and many legal or political hurdles on our part," he said. "I do not think we can finalize our policy making in a few days."

Nakasone also will discuss arms control with Reagan, especially his support for the "zero-zero" proposal to abolish medium-range missiles, officials here said. Japan was "strongly opposed" to an earlier proposal that would have allowed the Soviet Union to maintain 100 warheads in Asia, and Nakasone "certainly will express his appreciation" for the change, Matsuda said.

Nakasone, scheduled to step down by Oct. 31 after five years in office, will also address the United Nations and meet with Secretary General Javier Perez de Cuellar.