Prime Minister Yasuhiro Nakasone said today that Japan is prepared to bolster its defense ties with the United States to offset a growing Soviet military presence in the Pacific and will take "more drastic" steps to open its markets to foreign products before he goes to Washington later this month for talks with President Reagan.

In a question-and-answer session over lunch at his official residence here today, Nakasone told seven U.S. reporters that greater efforts to boost Japan's "self-defense capabilities should allow the United States to deploy its resources more effectively for the peace of the world."

Tokyo has been under mounting pressure by Washington to expand its defense role to help relieve heavy U.S. commitments in the military sphere, particularly by undertaking enlarged responsibilities for the protection of Japan's sea lanes.

While Nakasone gave no timetable for implementing a defense buildup, he pledged to honor a commitment made by his predecessor Zenko Suzuki for "even greater efforts" during talks in Washington with President Reagan in May 1981. He called the Suzuki-Reagan joint communique an "epoch-making one" and said Japan will gear its "defense strength to the changing international situation."

Nakasone's remarks came in sharp contrast to the more cautious stand of Suzuki, who fired his foreign minister and several top bureaucrats after they persuaded him to put the controversial word "alliance" into the communique to describe the military relationship between Tokyo and Washington. The phraseology touched off a storm of protest in Japan, where antiwar sentiments are strong.

Appearing relaxed and confident, Nakasone, who came to office Nov. 26, said "the Japanese people are gravely concerned about the Soviet military buildup" in the Pacific and specifically about the recent strengthening of military installations on the Soviet-held islands north of Japan, which Tokyo claims. He noted that the United States and its NATO allies "are rapidly developing their countermeasures" to Soviet moves, but indicated that greater efforts to "cultivate public understanding" on the defense issue in Japan would be necessary "to ensure that there be no abrupt shock."

Speaking through an interpreter, Nakasone, who has been known in the past for his hawkish views on national defense, stressed the "complementary nature" of Japan's military relationship with the United States under the 32-year-old mutual security treaty between the two countries. Asked if he foresaw any need to alter the terms of the existing arrangement, Nakasone said the revision of the security pact would "probably not take place" during his administration.

Nakasone, who has in the past advocated the revision of the anti-war provision of Japan's American-engineered postwar constitution, said today the question was not under consideration by his administration. But he added that, while the constitution had "remarkable aspects," it was "not perfect." The time has now come, he said, "for all of us Japanese to discuss our constitution, to take a fresh look at it."

Asked about Japan's thorny economic ties with the United States, Nakasone indicated that his Cabinet would enforce more sweeping steps to open Japan's markets to foreign goods following a meeting of key economic ministers here on Jan. 13. He hinted that the package may include further streamlining of customs and product standards and testing procedures.

Nakasone said his Cabinet was studying the possibility of drafting comprehensive legislation to do away with these so-called "nontariff trade barriers" and allow a wider range of goods to enter the market.

In the background is the estimated $20 billion U.S. deficit in trade with Japan in 1982 that has brought warnings from American officials that the Japanese should move early this year to set a timetable for action on the many trade issues between the two countries or face the enactment of protectionist legislation on Capitol Hill.

Nakasone stressed, however, that Japan has already "made very substantial efforts" to speed up tariff reductions and expand import quotas on a variety of goods. He said Tokyo has reduced or eliminated import duties on about 330 items since last May and he had personally ordered tariffs on tobacco, chocolate and biscuits substantially cut since taking office in November, despite stiff resistance from domestic interest groups and elements in his Liberal Democratic Party.

These measures, however, have so far failed to impress U.S. trade officials, who have been pressing for more dramatic action.

Asked why Japan continues to be singled out for criticism of its trade policies, Nakasone said "it's because our growth and expansion has been very fast, too fast, and--because of the high unemployment situation in the United States and Europe--people feel uneasy about our expansion." He said, "We have taken specific action and we continue to study what additional actions can be taken."

Nakasone stressed a need to strengthen relations with the United States and South Korea, since Tokyo, Washington and Seoul all have "a common future." He indicated Japan would step up efforts to help stabilize South Korea politically and economically by extending economic aid for Seoul's development programs. Nakasone is scheduled to visit Seoul next week, when he is expected to reach an agreement with South Korean President Chun Doo Hwan on a $4 billion aid package.

In regard to his Cabinet's endorsement last week of a 6.5 percent increase (not adjusted for inflation) in defense spending for 1983, Nakasone said the figure--which undershot expectations of Reagan administration officials--did not include pay raises for military personnel. He said the percentage figure would increase if pay hikes are approved this year.

Nakasone also said he looked for the further strengthening of friendly, three-way ties among Japan, the United States and China. He added, however, that "does not mean any suggestion of confrontation vis-a-vis the Soviet Union by these three nations banding together." His fundamental philosophy, he said, was that "without a firm and strong bond between Japan and the United States, no policies toward the Soviet Union or the Communist Bloc . . . will ever be successful."

In an apparent response to reservations expressed recently by Southeast Asian leaders over the possible dangers posed by a militarily stronger Japan, Nakasone said that the "complementary nature" of Tokyo's defense relationship with Washington should eliminate "any unnecessary fear or restlessness among our neighbors in Asia."

World War II, he noted, "left Japan isolated in the world. Today, we must find ourselves living as members of the world in the international environment."