Defense Secretary Caspar W. Weinberger repeated to leaders here today that the United States hopes Japan will take part in research into President Reagan's proposed antimissile defense system.

In a speech to the Japan National Press Club this afternoon, Weinberger also said that the Soviet Union harbors aggressive designs in Asia and had deployed "atomic cannons" on Sakhalin Island, which is just off Japan's northern main island of Hokkaido, and "nuclear-capable missiles" on a group of islands claimed by Japan and the Soviet Union but occupied by the Soviets. U.S. officials declined to discuss whether nuclear warheads actually were deployed, however.

U.S. officials described the cannon as a 152-mm type that can fire conventional or atomic shells. Eight have been deployed in positions from which they could fire on ships passing between Sakhalin and Hokkaido, the officials said. A total of 30 are expected to be deployed.

The missiles were said to be Scud surface-to-surface models, which were developed in the 1960s and also have a nuclear capability. Their 190-mile range would allow them to strike portions of Hokkaido, they said.

In meetings with Prime Minister Yasuhiro Nakasone and Foreign Minister Shintaro Abe, Weinberger offered continued U.S. consultation to help Japan decide whether to take part in the "Star Wars" program, known formally as the Strategic Defense Initiative (SDI).

"We think there is great technical genius in Japan, and we invite countries, including Japan, to participate," he said at the press club today.

Nakasone and Abe were reported by Japanese officials to have told Weinberger that the question would be discussed after a report from a 55-member Japanese fact-finding delegation now in the United States is received. It is the third such group from Japan to visit the United States.

For the past year, Nakasone's public stance has been that he "understands" the U.S. desire to proceed with the SDI program but will reserve judgment on Japanese participation pending study.

The United States has signed agreements on SDI cooperation with West Germany and Britain.

The program is controversial in Japan in part because many people here associate it with nuclear weapons, which were used against their country in 1945. The Japanese government has sworn never to possess nuclear weapons.

Nakasone's words suggest that he favors a Japanese role, both to demonstrate commitment to the alliance with the United States and to ensure that Japan is not left out of any technological discoveries that result from the research.

According to some theories, Nakasone will opt for keeping the Japanese government officially neutral but allowing Japanese private companies to take part in order to circumvent public opposition.

There has been speculation here that Nakasone wants to reach a decision soon, possibly before the economic summit with President Reagan and leaders of five other western industrialized countries from May 4 to 6.

Japanese government policy prohibits the export of weapons or arms technology. However, under a 1983 agreement, the government can give case-by-case permission for sale of military technology to the United States.

Despite opposition from local residents, the Japanese government is planning to build a runway on the island of Miyake for use in training U.S. pilots and housing for U.S. military personnel in the city of Zushi, near Tokyo. Weinberger thanked Nakasone's government today for its efforts on these issues.

Weinberger arrived in Japan Thursday from South Korea, where he reaffirmed U.S. determination to defend it from attack. A joint communique said the 1988 Olympic Games, which are to be held in Seoul, make the next two years particularly tense because Communist North Korea may try to disrupt them.

Japan will increase defense spending by about 6.6 percent in the year that began April 1. Though many U.S. officials would like to see a greater rate of increase, there is also a feeling in the Reagan administration that the current rate is substantial and the maximum possible given political constraints.