The Reagan administration's encouragement of a larger military role for Japan in the Western Pacific faces rough seas in Southeast Asia.
Washington is concerned about the growing Soviet naval strength in the area. It wants Japan to do more to defend itself and the vital sea lanes in the region.
But other Asian nations are worried that any significant Japanese rearmament would tempt Japan to revive its World War II aim of Asian domination. Some of them also express fears that an increased Japanese naval presence might eventually prompt Washington to reduce its own naval forces in the Western Pacific.
Of particular concern to such nations, is the US policy of pressuring Japan to build up its navy to cover a defense responsibility up to a 1,000 mile perimeter.
The US insists this would be measured from Tokyo Bay. But in Southeast Asia, especially in Indonesia, there has been concern that the zone could be measured from the southern tip of Okinawa - or, in any event, be gradually extended. This could give Japan control of important sea lanes leading toward strategic straits such as Malacca and Sunda, key points which Indonesia wants to control.
The Reagan administration remains convinced that Japan has no intention of dominating the region militarily. ''I don't think there is any indication whatsoever that the Japanese have any militaristic or offensive desire. . . ,'' said US Defense Secretary Caspar Weinberger on his trip over the past 10 days to Singapore, Thailand, and Indonesia, as well as New Zealand and Australia.
And some Asians themselves argue that a stronger Japanese Navy would help prolong the US naval presence in the region by sharing defense tasks and enabling Washington to cut some of its costs. (The US allocates about 6 percent of its gross national product to defense compared to an estimated rate of about 1 percent for Japan.)
Asian concerns became public during the September visit to Washington by Philippines President Ferdinand Marcos, who told television interviewers there is a danger a rearmed Japan might revive its World War II ambitions. During the October visit to Washington of Indonesian President Suharto, Indonesian officials sought US assurances that the push for Japanese rearmament would be limited.
Many Asian nations, however, recognize that there has been a gradual rise of Soviet military power in the Pacific.
According to the US Navy, some 80 Soviet surface combatant ships (destroyers, frigates, cruisers, and one helicopter carrier) are either deployed in or are deployable in the Pacific. That is up from 55 in 1968. In addition, the US Navy says the number of Soviet submarines capable of being deployed to the Pacific have risen from 105 in 1968 to 129 in today.
The US has a two-pronged answer to the Soviet naval presence in the Pacific. One is to strengthen its own naval establishments at Subic Bay in the Philippines, at Guam, and at Yokosuka and Okinawa in Japan. Another is to encourage Japan to do more of ''its share.''
If Japan did more to defend its surrounding ocean, including the nearby sea lanes for oil tankers that pass through the Malacca and Sunda straits, then US forces would be freer for deployment farther from Japan, the reasoning goes.
During his tour Mr. Weinberger discussed a range of issues, including the extent of US support to friendly nations if they were attacked by Soviet or Vietnamese forces. In Bangkok and Jakarta he declared American forces were adequate to match a growing Soviet naval presence in the Pacific and added that there had been no requests for an increase in US military activity.
But beneath the surface in some countries, questions remain over the reliability of the US military commitment, and over Japanese rearmament.
In an area where Japanese conquests in World War II were often brutal, there is growing suspicion of Japan's intentions. Some of this was triggered by the international textbook controversy touched off last summer when Japan's Education Ministry revised national textbooks to give a more positive view of Japan's actions in World War II.
There were official protests and demonstrations in many parts of Asia, and even by Chinese living in countries as far away as the US. An agreement to ''revise the revisions'' by the 1985 school year has cooled the controversy, but suspicions are still alive. Many in Asia took the textbook controversy as evidence that Japan cannot be trusted and that deep down its World War II ambitions have not really changed.
Japanese civilian and military officials have endorsed the concept of the 1, 000-mile defense perimeter. US officials describe this not as a change in Japan's mission to defend itself, but as an enhancement of its ability to do so. The Americans have expressed unhappiness over what they see as Japan's slowness in building the strength to protect the perimeter.
In Japan there is some unhappiness about the American pressure - both from anti-war groups which oppose military confrontation with the Soviets and from government circles which do not want quickly to shoulder a growing economic burden of defense. So, ironically, there is some agreement both in Japan and in Southeast Asia among those who criticize the American push.
There is also general agreement that the Soviet Pacific naval force is growing. But current strength of surface ships looks less formidable when compared to American forces.
The US force theoretically deployable to the Pacific is 97 surface ships, compared to 80 for the Soviets. This includes six US aircraft carriers (seven by December of this year) - compared to only one helicopter carrier for the Soviets - along with 14 American cruisers, 38 destroyers or guided missile vessels, and 39 frigates.
In submarine forces, the US appears to be at a substantial numerical disadvantage. Of the Soviets' 129 submarines available for deployment in the region, some 90 are nuclear powered; and, of these, about 30 are armed with ballistic weapons. The US has a total of 48 submarines deployable in the area, of which 44 are nuclear powered; an undisclosed number of these can fire nuclear-armed missiles.
The picture changes when the number of vessels actually deployed from bases in Vladivostok is considered. The US Navy estimates say that at any one time seven Soviet combat ships plus 13 support vessels are deployed in the more limited area of the South China Sea. (Soviet deployment figures for the entire Pacific are not given out by the US Navy.)
With the Americans, as with the Soviets, the actual number deployed in the Pacific is far lower than the potential of 145 surface ships and submarines. As of Nov. 3, Pacific deployment was put at 70 ships - including two carriers, four cruisers, eight submarines, and 17 support ships.
The Soviets are aided in their slow naval buildup by service facilities which Vietnam has agreed to provide at the former American base at Cam Ranh Bay. US Naval officials say access there makes it easier to service and support its patrols, which typically total 20 ships in the Indian Ocean and 20 ships in the South China Sea. They say the Soviets could do this without Cam Ranh, but with greater difficulty. Cam Ranh facilities also help extend the limited range of diesel-powered Soviet submarines, which need frequent stopovers.
Perhaps the greatest signficance of Vietnam's decision to allow Soviet use of Cam Ranh is hypothetical. American naval experts maintain that if, in the event of war, Vietnam agrees to expand concessions at Cam Ranh Bay, the Soviet Navy's range and speed could be vastly increased.