At this lovely seaside resort, the foremost reminder of Japanese efficiency is a robotized swimming pool: Because ocean swimming in this area is dangerous, the Japanese have installed pumps making synthetic "ocean" waves almost as invigorating as the real thing. And there is no messy sand.

But the gentle ripples at poolside disguise bigger ones inside the conference rooms at the Oiso Prince Hotel, site for the fifth Shimoda meeting (so named because the first one was in that city). This conference, bringing together key Japanese and American officials in a private forum, is ventilating the extraordinary pressure being placed on the government of Prime Minister Zenko Suzuki by President Reagan to increase Japan's defense commitment.

The Japanese are doing their best to fend off American demands for a big increase in the Japanese military budget, which is only about $10 billion, or less than one percent of their gross national product. The Japanese do not feel as directly threatened by Russian power as do the hawks in Washington, and they feel quite keenly that Reagan was overreacting when he proposed a $1.5 trillion military commitment from now until 1986.

The opinion-makers in Japanese society, many of whom are at the Shimoda-Oiso conference, do not see Soviet expansion as a threat to Japan. They are much more concerned with potential tensions in the Middle East, which might shut off the flow of petroleum that provides 70 percent of Japan's needs. At a time when the United States is engaged in a tense struggle with Libya, Japan is buttering up that oil producer with excessive praise of Libya as "a truly democratic society" on the occasion of the 12th anniversary of the Libyan revolution.

Thus, Japan seeks an accommodation with the Organization of Petroleum Exporting Countries, and seems to believe, naively, that if the United States would only pressure Israel to give back the occupied Arab territories and make peace with the Palestine Liberation Organization, oil would flow unimpeded from the Persian Gulf.

This ignores all the other potential upsets in the tinderbox that is the Middle East. But there is a certain shortsightedness on the American side, as well. For example, the pressure for a substantial increase in Japanese military expenditures stems almost exclusively from U.S. budget pressures back home, without any real thought of what Japan would defend itself against, how the money would be spent, or where. And as some of the more thoughtful Americans at this conference have been saying out loud, our State Department seems to have given no thought to just how far the United States wants to go in pushing Japan, once again, into a role as a commanding military power.

The Japanese once swung their military weight aggressively through Asia and across the Pacific with humiliating and disastrous results. Since their defeat in World War II, they have rebuilt their power, but on the economic side. There is little real thirst in Japan to do anything that would disturb their enormous economic success.

The Japanese would rather lead an invasion with computers, integrated circuits, automobiles and robots than with guns, aircraft or missiles.

Yet, the history of U.S.-Japanese relations since the end of World War II suggests too easy a responsiveness to American demands and pressures. And the hints one gets here suggest that this may again be the case. Already, the Suzuki government (to the dismay of generally dovish public opinion) has quietly introduced fiscal 1982 expenditures for interceptor fighters, antisubmarine patrol planes and antitank attack helicopters, which will show up in substantially big spending numbers in future years.

What makes this gradual buildup of Japanese military strength especially offensive to some sectors of Japanese society is that it comes at the precise moment that the West German government is cutting its overall budget to the point that Bonn will fall short of meeting its NATO target of a 3 percent annual increase in military outlays.

"Just after the war, we had a good idea of what the Japanese could do on the economic side if they concentrated on it," says an American long on the Tokyo scene. "We ought to take satisfaction at what they've accomplished in the economy instead of screaming at them for their successful performance. But now, for short-term budget-balancing considerations, we're pushing them -- against all their own instincts -- back into a military posture.

"I don't think we have given any thought to the long-term implications. I can just see the 1990 headline: 'U.S. and Japan Fight Over Share of Subsonic Missile Business in Malaysia.' Then tell me how smart we've been."