On Easter Sunday, 40 years ago, American forces landed on the island of Okinawa in the South China Sea to begin the last great battle of World War II. It was to be the bloodiest of the Pacific fighting: Eleven weeks later, when Okinawa fell, nearly 13,000 Americans were dead, another 40,000 were wounded and 110,000 Japanese had lost their lives. In a few weeks came the flight of the Enola Gay over Hiroshima, during which the atomic bomb was dropped. Three days later Nagasaki was bombed. Then came swift surrender, the signing of peace accords on the deck of the battleship Missouri in Tokyo Bay formally ending World War II, and the American occupation of Japan.

Two generations have passed. One of the great stories of that postwar period has been the way the two former blood enemies, the Americans and the Japanese, put aside the hatreds spawned by Pearl Harbor and Hiroshima and developed a remarkable relationship of mutual respect and partnership.

There have been strains and problems between the two, but nothing has approached the sudden venting of American anger at Japan in Washington in recent days. The comments go far beyond trade and economic policy questions, however serious those may be. They have a raw and violent edge about them, dredging up racial and cultural animosities. They recall the cast of mind of those bloody days of World War II.

At a private dinner last week I heard a distinguished public servant tell a group that included members of the House and Senate, other officials and prominent people from Wall Street of a remark allegedly by someone in the White House: "The next time B52s fly over Tokyo, we better make sure they carry bombs."

The next day I saw a congressman address his colleagues: "We are in a war. This is only the first shot. After this passes, I think we are going to have to load the gun and put some real bullets in it . . . . "

Similarly heated rhetoric hung, it seemed, everywhere in the spring air of Washington. Why this outburst? Why now, and what does it mean?

No one I've spoken with lately offers as rational an analysis of this deeply troubling phenomenon as Prof. Jay W. Forrester of the Massachusetts Institute of Technology, whose work on world and urban dynamics, and analysis of world economic trends, have attracted international acclaim and controversy for many years.

"I think we are putting too much emphasis on how to cope with the Japanese and not enough on how to put our own internal house in order," Forrester says.

In other words, we're not dealing with our great trade deficit, our great federal budget deficit, our overvalued dollar and the inefficiency of our outmoded industrial base. Members of Congress know all this and are reacting, partly at least, out of frustration at our inability to resolve these problems.

During a lengthy conversation late last week, Forrester offered other observations about this flaring of anti-Japanese feelings:

"I think it may be largely motivated by internal stress that people don't want to face up to. It is a classic process of blaming somone else for one's own internal difficulties in trying to rally the public against an external imagined enemy rather than facing up to the internal problems. It is my feeling that the threat to the United States is very much greater from the dislocations and uncertainties in our internal economy than it is from any external threat, economic or military. So there's just a sense of frustration, of not knowing what to do, of not undertanding what's going on. I think the public would like to know what's happening even if it's uncomfortable to face up to it."

Forrester's present work with computer models on economic trends ("systems thinking" in which he has pioneered) leads him to some arresting -- and disturbing -- conclusions:

"Our work says that we're in one of those transition periods, or a gap in between periods of economic growth. The 1930s were such a period -- a period when the old technologies were pushed as far as they could be, when debts were overextended as a result of the prior expansion and as a result of excessive credit creation. Then a day of reckoning comes, as you see in the Farm Belt at the present time . . . . "

That, in his view, adds up to new tensions and rising frustrations.

"I anticipate that we will have a decade of economic crosscurrents," he said. "Since 1965 we've had increasingly severe business-cycle ups and downs. This present recovery is probably going to run its course sooner than the previous recoveries, with the chance that the following downturn will be very likely deeper than the 1982 one, which has considerable impact on plans for the federal deficit. We'll be moving into a situation where revenues are going to be under pressure and costs will rise so the likelihood of an increased deficit is pretty strong, I think.

"It's not possible to say exactly when a recovery will top out. It's my belief that this recovery will not run as long a course as the previous several. If that's true, then within the next year or two we will be quite clearly past the peak of this business cycle recovery with a fairly good chance the economy will seem in much less good shape in two or three years from now.

"We need to face up to what we're going to do about massive defaults in the banking system. The Latin American debts are going to get into greater difficulty. My feeling is they're essentially certain to be defaulted on in time, and they are, of course, about the same order of magnitude of the net worth of the American banking system. So, potentially, that is a severe shock to the system. The loans on our agricultural lands are in similar jeopardy, and they are greater than the Latin American debts. I don't see much happening to prepare the public for that kind of dislocation. And it's apt to shape up very suddenly when it starts."

Forrester is no pessimist. For all I know, his economic analysis may be all wet. But Washington politicians and policy-makers, from Capitol Hill to White House, could do worse than ponder something else he said:

"I'm not prepared to say what we should do to minimize the disruption, but certainly to face the reality is a first step. Over-optimism can be a great disservice. You know, the history of the rise and fall of economic activity back through the 1800s has been that politics go liberal during the expansion phases. Excesses develop and then, as one reaches a peak period as in the late 1970s, there's a tendency for politics to go conservative and social and ethical values to turn traditional. The Moral Majority is exactly on schedule. Then the conservative politician steps forward at the peak and is there at the beginning of the downturn, as President Herbert Hoover was, to take the full blame. I think the odds are very good that this administration will run into that trap."

This Easter Sunday anniversary of terrible American-Japanese combat in the Pacific ought to be an occasion to recall the tragedies of the past and to act anew in avoiding them. I, for one, find Jay Forrester's plea for realism not only refreshing. In today's world, it is indispensable.