The United States deployed its military forces for political impact abroad at least 215 times in the three decades since the end of World War II, an extensive study by the Brookings Institution reported yesterday.

During the same period the Soviet Union deployed its military units on at least 115 occasions, based on less complete reporting, the study said.

The United States "show of force" by ships, aircraft or troops was successful in most cases from the viewpoint of the policymakers who ordered it - but this usually "bought time" for further decisions or actions without changing the situation in fundamental way, according to the study by Brookings' Barry M. Blechman and Steven S. Kaplan. Their report was the product of two years research on a $180,000 contract of the Pentagon's Advanced Research Projects Agency.

The Korean and Vietnam wars as well as routine military operations were excluded from the study, which focused on the use of military force to influence the behavior of another nation without engaging in a continuing contest of violence. In most cases, the action was limited to the threat of force, with no shots having been fired.

Blechman, who is serving as transition aide for the Carter administration with the Office of Management and Budget, said in an interview that he was surprised at the large number of incidents in which U.S. "show of force" was employed. The Brookings research and report were based on unclassified sources, but Blechman said a study using secret materials by the Center for Naval Analysis produced a strikingly similar list.

Among the incidents listed by Brookings researchers was the positioning of a U.S. naval task force of Brazil in early 1964 to support a coup by that country's armed forces against the leftist government of President Joao Goulart. The maneuver was reported in detail in The Washington Post last week on the basis of recently declassified documents from the Lyndon B. Johnson presidential library.

One of the earliest incidents was the dispatch of the battleship Missouri to Turkish waters in early 1946, ostensibly to return the body of the Turkish ambassador who had died in Washington (but was actually to deter threats to Turkish independence by the Soviet Union).

The most recent incident in the report was the powerful naval and U.S. Marine Corps task force sent in connections with the rescue of the U.S. merchant ship Mayaguez in Cambodian waters in May, 1975. ALthough there have been several "show of force" maneuvers since then - notably air and sea forces sent toward Korea after two American officers were killed in a demilitarized zone incident last August and U.S. forces sent to back up Kenya last July after threats from Uganda - the cutoff date for the Brookings compilation was Oct. 31, 1975.

U.S. strategic nuclear forces were deployed for political effect in 33 instances, mostly in the 1940s and 1950s, according to the report. The last instance of a nuclear threat listed in the study was the worldwide U.S. alert ordered during the October, 1973 Middle East war in an effort to deter Soviet participation. This and the 1962 Cuban missile crisis were the only two "overt and explicit threats" of nuclear force directed at the Soviet Union, according to the report.

When a U.S. aircraft was downed over Yugoslavia in 1946, six B-29s flew "rather ostentatiously and menacingly" along the Yugoslav border, according to the report. Nine other instances involving strategic nuclear forces were movements or alerts of Air Force strategic bombers involving tensions with the Soviet Union or China. Strategic Air Command bombers were flown to Uruguay in 1947 and Nicaragua in 1954 with the apparent intention of reassuring U.S. allies.

From the mid-1950s to the mid-1960s was the most active period for U.S. political use of military forces abroad, according to the report. An average of 13.4 incidents per year took place during the presidency of John F. Kennedy, an average of 19.7 incidents yearly during the Lyndon B. Johnson administration, 7.3 incidents yearly during Dwight D. Eisenhower's presidency but 5 or fewer incidents yearly under Harry S. Truman, Richard M. Nixon, and Gerald H. Ford.

Naval units participated in four out of every five of the incidents, land-based air units in about half, and ground combat units participated in one-fifth of the "show of force" incidents. The analysts reported that, in general, the greater the U.S. commitment implied by the forces assigned, the more successful was the impact and result. The use of strategic nuclear forces and American forces actually landed on foreign soil implied the greatest commitments, and also were accompanied by the greatest risks.

An examination of Soviet use of armed forces for political impact abroad suggested that the Russians have been more active far from home after the achievement of rough strategic party with the United States around 1969. The report said Soviet military personnel have participated in three conflicts since the late 1960s - the Egyptian "war of attrition" against Isarel, the civil war in Sudan, and and Iraq's war against the Kurds.

On the other hand, the Russians have almost never instigated the crises in which they have intervened since 1968, the report said.

Even in the Middle East, where the Soviets have encouraged Arab hostility to Israel, tensions have grown more fundamentally out of local issues, according to the study. In general, Soviet use of military forces for political effect has been less provocative in its challenge to U.S. interests under party leader Leonid I. Brezhnev than in the Nikita Khrushchev era, according to the study.