The Reagan administration in its second term should use "paramilitary assets" to weaken the governments of Vietnam, Cambodia, Libya and other unfriendly nations around the world, the Heritage Foundation said in a report presented to the White House last week.

"Where U.S. geostrategic interests are threatened, it is incumbent upon the United States to provide positive measures to influence the direction and pace of such change," the report stated.

The operations are envisioned as part of a stronger U.S. posture in the world, which the report said also rests on continuation of a military buildup, redoubled efforts to build defenses against missiles and a strong suspicion of the value of arms control talks. Other countries where the United States should intensify or begin covert operations include Laos, Angola, Ethiopia, Afghanistan, Nicaragua and Iran, according to the report.

The recommendations on paramilitary action are contained in "Mandate for Leadership II," a compendium of more than 1,300 proposals for President Reagan's second term put together by the conservative Heritage think tank. A similar volume published four years ago presaged many of the policy initiatives of Reagan's first term, although not all of the proposals were followed. The foundation urged an expansion of U.S. covert operations four years ago, but in more modest terms than in the current document.

The sections of the report on defense and arms control, scheduled to be released today, strongly support the administration's efforts during the past four years to modernize the U.S. military. The report said that the buildup must continue and that the administration should buy more of some weapons, such as the B1 bomber, than now planned.

At the same time, the report sharply criticized Pentagon management during the first term and said the defense secretary should take charge of efforts to improve the way weapons are purchased. The report said that the administration's past "acquisition initiatives" have "not proved particularly effective."

"While substantial progress has been made in force modernization in the last four years, more now needs to be done to fix the way America does its defense business and spends its defense dollars," the report said.

The Heritage report strongly urged the administration to abandon the Anti-Ballistic Missile Treaty, which the United States and Soviet Union signed in 1972, and move swiftly to develop weapons that could defend MX missile sites against attacking missiles.

This would require a "restructuring" of Reagan's Strategic Defense Initiative, often referred to as "Star Wars," which seems to be emphasizing longer-term research projects aimed at wide-area defense. While supporting those research efforts, the report said the Pentagon should move as quickly as possible to deploy "point-defense" weapons around "high-value military targets."

The report's disdain for the ABM treaty holds true for most other arms control efforts. Heritage experts say that the United States should not negotiate over antisatellite weapons or any form of strategic defense; should not seek a comprehensive test ban treaty and should not ratify the Threshold Test Ban Treaty; should no longer abide by the guidelines of the unratified SALT II treaty, which both the United States and Soviet Union have said they would respect; should not seek a treaty banning chemical weapons, which would be "virtually impossible" to verify, and should not make new proposals in the stalled talks on strategic missiles, medium-range missiles or troop strengths in Europe.

"Arms control policies based on the hope that negotiations with Moscow will lead to agreements that effectively limit the major instruments of Soviet military and diplomatic power are unrealistic, lead to a false sense of security and do not protect the American people," the report stated. "A new era in arms control is beginning, based on the development of defensive systems to protect the United States and its allies from Soviet missile attack."

The report supported funding for more planes, ships, tanks and other weapons, including some that the administration has not yet proposed or has not persuaded Congress to fund: chemical bombs and rockets, C17 cargo planes, a new, turretless tank to replace the M1 Abrams and Northrop Corp.'s F20 Tigershark fighter jet, which was developed for export but has not been sold.

The one exception is the Army's DIVAD antiaircraft gun, which Pentagon officials say has performed poorly in early tests.

The report said that the administration should "employ paramilitary assets to weaken those communist and noncommunist regimes that may already be facing the early states of insurgency within their borders and which threaten U.S. interests."