Dramatic changes in the allocation of power among nations in the next two decades will require major shifts in the national security strategy of the United States, according to a 15-month study by an advisory commission to the National Security Council and the Department of Defense.

The report of the Commission on Integrated Long-Term Strategy to be presented to President Reagan Tuesday calls for a greater emphasis on meeting the threats of regional conflicts including limited, nonnuclear attacks by the Soviet Union in the Persian Gulf or other areas far from NATO's central front. Accounts of the report are being published today by a number of news organizations following a Washington Post story in yesterday's editions based on a preliminary draft of the document.

By the year 2010, the commission reported, the United States will still be first in total economic output (gross national product) by a wide margin, but the Soviet Union will be a poor fourth in this index of national power. The second-ranking nation in economic output, according to the projection, will be China, which is forecast to have surpassed Japan by a small margin at that time.

The commission's report on economic trends, based on Rand Corp. studies, said Japan recently passed the Soviet Union to become No. 2 in the world in total economic output.

Because of these and other shifts, "lesser powers will acquire advanced weaponry, diminishing the relative advantages of both U.S. and Soviet forces," said the report.

In the future even more than in the past, the commission said, a massive Soviet-bloc attack on Central Europe or an all-out Soviet nuclear attack on the United States will be "much less probable than other forms of conflict" even though those two high-profile threats have dominated U.S. military planning and North Atlantic Treaty Organization policy.

In an era of tight military budgets, the United States in the near future should "accept a greater risk of the unlikely extreme attacks, in order to bring about a reduced risk of the more probable conflicts," according to the report.

A central message of the report, titled "Discriminate Deterrence," was a call for more selective preparations for military action using "precision weapons" made possible by dramatic improvements in accuracy brought about by computers and microelectronics.

Albert Wohlstetter, co-chairman of the commission and director of research for Pan Heuristics, a West Coast think tank, said the "silent revolution" in accuracy makes it possible for cruise missiles fired from thousands of miles away to be programmed with confidence to land within 10 yards of a previously identified target. Current technology makes possible accuracies of one to three meters (about three to nine feet) against fixed targets "at any range," the report said.

In this situation, the size of the explosion needed to destroy a given target can be drastically reduced. By 1995, the report said, nonnuclear explosives will be able to substitute for atomic warheads in intercontinental ballistic missiles and still destroy hardened military targets.

The revolution in accuracy is an essential reason for a sharp decline in the total explosive power, or yield, of both the U.S. and Soviet nuclear arsenals over the past decade. A major consequence of this trend, which is only hinted at in the report, is that a 50 percent cut in U.S. and Soviet strategic arsenals envisioned in a dramatic new START (strategic arms reduction treaty) agreement could be accomplished with a minimum cut in military effectiveness of the two nations.

While couched in restrained language, some of the commission's recommendations and observations are likely to be controversial. These include:More emphasis on preparing essentially offensive military actions, including "conventional counteroffensive operations deep into enemy territory" in case of war. A shift in space policy toward much larger numbers of smaller, cheaper satellites usable for combat operations but not for the highly sophisticated "spy in the sky" activities of the peacetime U.S. reconnaissance satellite program. The possible shift of "special activities," also known as "covert action," from control and supervision by the CIA to that of regional U.S. military commanders under the aegis of the Pentagon. The use of "cooperative forces" of Third World allies of the United States to combat the Cubans and others in the Soviet bloc who work for Moscow in the developing world. No countries were named as likely sources of such forces.

The 13-member commission was co-chaired by Wohlstetter and Undersecretary of Defense Fred C. Ikle. The commissioners, all currently outside government except for Ikle, included former secretary of state Henry A. Kissinger, former White House national security advisers Zbigniew Brzezinski and William P. Clark, former chairman of the Joint Chiefs of Staff John W. Vessey and other establishment figures in the defense and diplomatic fields.

Such publicly funded examinations of U.S. long-term strategy are rare and most of these have centered almost exclusively on a massive Soviet nuclear attack or large-scale conventional war. The 13 previous efforts at national strategic planning identified by the Pentagon include "NSC 68," the planning document for the Cold War written in 1950, the Gaither Committee report of 1957 calling for a U.S. strategic nuclear buildup, the Acheson report of 1961 on NATO policy and the Carter administration's "PD-59" of 1980 proposing changes in U.S. nuclear weapons targeting.

The theme of many of the earlier documents was an eroding U.S. military balance in relation to the Soviet Union, growing U.S. vulnerability to attack and a growing risk of war between the nuclear superpowers.

The new commission report, while seeing many threats to U.S. national security, suggests that various trends will bring a lessened reliance on powerful nuclear weapons, a shrinking degree of U.S. and Soviet control over regional conflicts and a sharply declining economic base for Soviet power compared with that of the United States.

An overriding message in swiftly changing circumstances, said the report, is "the need for flexibility in the U.S. defense posture."