The Japanese government, under pressure from the United States to strengthen its military capabilities, today outlined a five-year defense program estimated to cost $62 billion to $65 billion, including an $18 billion increase in spending on advanced weapons.

The program will give Japan the power to turn back "limited and small-scale aggression" as envisioned in the country's 1976 basic defense plans, according to government officials and private defense analysts here. It will provide for greater protection of vital sea lanes and air space around Japan by introducing substantially more F15 fighters, P3C antisubmarine planes and other sophisticated military hardware.

Senior Japanese defense officials suggested, however, that the new spending plans may fall short of U.S. expectations. They acknowledged that the program was not likely to be adequate to provide for the total defense of sea lanes and air space up to a distance of 1,000 miles from Japanese shores--the commitment sought by the Reagan administration to help offset the burden of U.S. military responsibilities in the Pacific.

Haruo Natsume, director general of the defense agency's policy bureau, told reporters that despite Japan's increasingly critical military situation, the nation's defense capabilities were now far below those described in the 1976 defense outline. He said that the new defense buildup plan would bring "remarkable improvement" in existing military capabilities.

The plan for the 1983-1987 period was approved by the Japanese National Defense Council, presided over by Prime Minister Zenko Suzuki. It is intended as a broad guideline for military spending budgets, which will be subject to yearly approval by the Diet, the Japanese parliament.

If all goes smoothly, officials said, Japan will strengthen its air and sea defenses with the purchase of 75 F15s to add to 80 planes already ordered. The plans also provide for the purchase of an additional 50 P3Cs beyond the current authorized level of 25 aircraft, plus 14 antisubmarine warships, 6 submarines and 13 minesweepers, which would give Japan one of the world's largest antisubmarine warfare capabilities.

Defense analysts here say that the completion of the program could give Japan the world's sixth largest conventional naval force, after the Soviet Union, the United States, Britain, China and France.

Officials said that the five-year plan represented the best effort possible under Japan's current fiscal austerity drive. Officials declined to say what portion of the military hardware might be directly purchased from producers in the United States or manufactured in Japan under licensing agreements with American firms, although private analysts here said a substantial portion of new contracts would go to U.S. producers.

The new five-year defense outline has been the subject of a sharp debate in recent months between Japan's defense agency and its tight-fisted Finance Ministry, which is determined to reduce Japan's huge cumulative budget deficits by curtailing government spending. The roughly $18 billion earmarked for major military equipment purchases is well below the defense agency's initial request of about $23 billion.

Despite mounting American pressure in recent years for an expanded Japanese defense role, military spending in Japan has been constrained by the antiwar provisions of Japan's postwar "peace" constitution and an unwritten but widely accepted government guideline that defense outlays not be allowed to go beyond 1 percent of the country's gross national product.

The 1 percent ceiling was originally set in the mid-1970s by former prime minister Takeo Miki's cabinet in the wake of a public outcry touched off by a multi-million-dollar scandal allegedly involving influence-peddling by high government officials in major aircraft sales contracts.

The government's disclosure today that fulfillment of the five-year defense plan may require spending beyond the 1 percent ceiling, however, has raised only a minor public reaction so far. Private analysts here say that the absence of a public outcry reflects wider acceptance of a larger defense role for Japan.

Defense officials here estimated that the new five-year plan will require yearly increases of between 6.5 and 8 percent in appropriations for defense. Such increases, they say, may represent anywhere from 0.97 percent to 1.02 percent of GNP, depending on the overall yearly growth of the Japanese economy.

These official estimates are based on a yearly growth rate of 5.1 percent for Japan's economy over the next five years, although private economists here say that the figure may be closer to 3 percent as a result of current dour economic forecasts. Lower economic growth, defense analysts say, could make it difficult to achieve the new military spending plans.

In contrast to the roughly 5.9 percent of GNP the United States spends on defense, Japan's roughly $11 billion military budget for the current year represents a 0.93 percent share of GNP. The pace of Japan's defense spending has gathered speed in recent years, however, and now outstrips yearly increases in the country's spending on practically all other key budget categories.

Earlier this month, Tokyo proposed a 7.34 percent increase in its military budget for 1983 and at the same time called for cutbacks of about 5 percent in appropriations for other key government departments. The 7.34 percent increase in military spending, if formally approved later this year, would be slightly less than this year's 7.75 percent increase.

In upping the defense ante, the Suzuki government's chief concern appears to be what is perceived here as sharply rising U.S. criticism over Japan's yen-pinching military budgets and the record surpluses it continues to pile up on trade with the United States.

Japanese defense officials said Japan's medium-term military spending plans reflect a growing concern in Japanese political circles over Soviet military expansion in the western Pacific.

One senior defense analyst said, however, "The government is slowly endeavoring to improve defense capabilities as a result of U.S. pressure. Right now, that pressure is far more important than any perception of a Soviet threat."

Pentagon officials have stressed that the United States does not want to see Japan become a military superpower but have requested that Japan undertake greater responsiblities for an expanded defense role.

Commenting on the new five-year plan, the U.S. Embassy in Tokyo said: "While the Japanese government must balance its commitment to strengthen its defense capabilities with due consideration for domestic, political and economic constraints, we will continue to encourage it to make the decisions necessary to further implement our mutual goals of closer and more effective defense cooperation."