Joao Baptiste, a foot soldier in the Angolan rebel army of Jonas Savimbi, watched in horror one day last August as a Soviet T62 tank broke through the dense bush in eastern Angola, firing at his fellow guerrillas and crushing one of them beneath its clanking treads.

Armed only with an automatic rifle and a grenade, Baptiste scrambled up the side of the tank, yanked the turret lid up and dropped the grenade into the hatch, according to accounts later told and retold in Washington. The explosion stopped the tank's attack on the lightly armed soldiers in Battalion 07 of Savimbi's guerrilla army, which has been fighting the Soviet-armed Marxist regime for a decade.

Such tales of heroic "freedom fighters" pitted against vastly superior Soviet weapons -- the Rambo archetype in the Angolan bush -- have captured the imagination of President Reagan and provided the administration with an emblem for a new direction in U.S. foreign policy that conservatives have begun calling "the Reagan doctrine."

It is a doctrine that seeks to roll back Soviet and Cuban gains in the Third World by supporting anticommunist insurgencies. To translate theory into practice, the administration has turned to a Central Intelligence Agency reinvigorated and greatly expanded under the activist leadership of William J. Casey.

The former international banker and lawyer has unsurpassed stature among senior Cabinet members, making him perhaps the most influential CIA director since Allen W. Dulles in the 1950s in shaping American foreign policy. Casey has used that influence and his own enthusiasm for covert operations to expand CIA paramilitary involvement in Nicaragua, Afghanistan, Cambodia and now Angola.

The resignation last week of CIA Deputy Director John N. McMahon, who reportedly was wary of American entanglements in the Third World, appears to have removed one of the principal brakes in the agency against such growing operations.

Since Reagan took office in 1981, Casey has rebuilt the CIA into a lethal and controversial instrument for carrying out covert operations. The agency's annual budget for secret missions far exceeds $500 million, far higher than at any time since the Vietnam war. The administration's request for $70 million to underwrite the rebels fighting the Sandinista government of Nicaragua would push the sum even higher.

In recent months, the administration has established a secret interagency committee to oversee the increasingly complex patchwork of covert operations. Although formally nameless, the group meets in Room 208 of the Old Executive Office Building and sometimes refers to itself as the "208 Committee." Its members are the micromanagers of America's new secret diplomacy, supervisors of a widening array of local conflicts around the globe where American and Soviet interests collide.

These brush-fire wars -- known as low-intensity conflicts in military jargon -- have come to dominate Reagan's foreign policy agenda in his second term. Some officials believe that they will be the main battleground of East-West rivalry for years.

Information for this article was gathered during several weeks of interviews with officials in Congress, at the White House and in other government agencies including the State and Defense departments. Other information was provided by sources with past or current connections to the U.S. intelligence agencies. Some information was drawn from published accounts. In many instances, officials spoke only on the condition that they not be identified.

Reagan's interagency group resembles in many respects the legendary "40 Committee" established in the Nixon administration to manage an earlier set of secret wars in the 1970s. The 208 Committee meets periodically to determine which weapons will be shipped, which secret warehouse goods used, which middlemen will deliver them to clandestine airstrips. The committee sets budgets, goals and timetables for each operation, again with the CIA serving as the principal agent.

Members of the committee include Donald R. Fortier, deputy national security affairs adviser; Clair George, head of the CIA's clandestine service; Michael H. Armacost, undersecretary of state; Fred C. Ikle, undersecretary of defense for policy, and Morton I. Abramowitz, head of the State Department's Bureau of Intelligence and Research. Regional experts are summoned as needed to serve on subcommittees; decisions are ratified by the National Security Planning Group, consisting of the president and his key national security affairs advisers.

They have plenty to do, according to informed sources. Around the globe, the CIA's new activism can be seen in a number of ways other than its covert paramilitary role. In Chad, the agency helped engineer the rise to power of Hissene Habre. In Liberia, it provided security assistance to President Samuel K. Doe. In Ethiopia, Suriname and Mauritius it has dabbled in opposition politics.

The newest and most sensitive covert program targets Libya. CIA and Pentagon planners are working with the opposition and Libya's pro-American neighbors to destabilize the regime of Col. Muammar Qaddafi, who has been denounced by the administration as a patron of international terrorism.

At its heart, the Reagan doctrine seeks a historic turnabout in which American aid underpins a new generation of national liberation struggles aimed at throwing off what American conservatives have dubbed "Soviet colonialism."

The policy, coincidentally, mirrors a Soviet doctrine unveiled a quarter-century ago. In 1960, Soviet party leader Nikita Khrushchev warned the West that Moscow's military muscle would be thrown behind "wars of national liberation" in the Third World, where colonial and leftist groups were struggling against colonial or pro-American regimes.

The resort to an increasing number of undercover operations run by the CIA has drawn fire from conservatives and liberals in Congress worried that covert action with obscure U.S. objectives is becoming a substitute for a well-defined foreign policy. The critics also worry that the agency once again will bog down in "dirty little wars."

Not only are Democrats mobilizing to block the new trend, but also the House and Senate intelligence committees have voiced alarm. Committee leaders are pushing to openly air the secret diplomacy; they want a congressional majority to either endorse or reject each paramilitary venture.

Much of the congressional anxiety centers on the complaint that covert paramilitary operations -- secret wars -- are initiated by the White House which then informs the congressional oversight committees. Under law, the committees are powerless to halt the operations and many members would like to absolve themselves from the appearance of consenting to such controverial undertakings.

Over the past year, presidential rhetoric has elevated the U.S. commitment to these anticommunist movements from moral and political backing to the resounding proclamation in Reagan's State of the Union message last month: "America will support . . . with moral and material assistance your right not just to fight and die for freedom but to fight and win freedom."

In his speech Feb. 26 justifying the administration's defense budget, Reagan used a map with arrows darting across the globe to pinpoint pro-Soviet Marxist regimes around the world. "We set out to show that the long string of governments falling under communist domination was going to end. And we're doing it," he said.

Despite this apparent escalation in administration commitment, there is still scant evidence that either the CIA or any branch of the armed services is gearing up to make a military victory possible through major U.S. support for any of these insurgencies, administration officials acknowledged. Nor is there analytical support among many -- perhaps most -- intelligence officers showing that military victories are likely in the conflicts despite the increased CIA presence.

Proponents of the Reagan doctrine argue that the potential for real military gains is being undercut by resistance at the CIA, the State Department and the Pentagon by bureaucrats leery of involving the United States in uncertain wars with uncertain public support.

In fact, public enthusiasm for the goals of the Reagan doctrine seems elusive. A December sounding by Republican pollster Robert Teeter found that "arming freedom fighters" was at the bottom of the list of national concerns for most Americans, a list topped by concerns about unemployment, arms control, inflation, deficit spending, national defense and tax revision.

Indeed, interviews with administration national security officials suggest that the most convinced advocate for the winning strategy recently articulated by the president is Ronald Reagan himself. Some officials believe the policy's real value is in "bleeding the Russians" at low cost to the United States. Others regard these Third World conflicts as bargaining chips in U.S.-Soviet negotiations.

There is even sharp disagreement in the White House about whether the administration should formally adopt the term "Reagan doctrine" to describe its "freedom fighters" policy.

At a recent Defense Department-sponsored conference, White House communications director Patrick J. Buchanan repeatedly used the term. "I think what you are getting at in the Reagan doctrine," Buchanan explained, "is that wars of liberation can be conducted against the extremities of the Soviet empire by people trying to recapture their country for freedom or for liberty."

However, Fortier, the president's deputy national security affairs adviser, disagreed. "We are not eager to see it labeled as a doctrine because the cases are complex and no rigid set of answers or mechanical formula can be applied," he said in an interview. "Still, the pattern of activity we are now seeing is quite real and we have a coherent policy for dealing with it."

Regardless of the label, Fortier said that the two primary impulses behind "a policy" are "promoting democracy and regional stability." To reach a U.S. objective of "national reconciliation" in these conflicts, Fortier said sustained U.S. pressure is essential.

"Obviously if we don't mount and sustain credible pressure over time, the Soviets are not going to reassess," he added, "but the point is to reach a solution, not just to drain them indefinitely in these areas for the sake of doing it."

However, the principal objective of "national reconciliation," so often cited by Reagan and his advisers, has virtually no successful precedent in post-World War II global politics. Nowhere has a hardened Marxist-Leninist government agreed to form a coalition with its anticommunist or democratic opponents or hold free elections.

Despite the administration's rational construct, the evolution of U.S. involvement in the four principal insurgencies under way today has been marked by shifting objectives and ad hoc decision-making, often in response to domestic political pressures.

In Afghanistan, Reagan inherited from the Carter administration a policy of aid to the resistance to the Soviet invasion in December 1979. Under Reagan, CIA funding of the Afghanistan resistance has leaped from less than $100 million to almost $500 million annually, but the White House has resisted congressional demands to double the administration's budget request.

Nicaragua marked the first major administration initiative toward anticommunist resistance movements. The program began in 1982 as a plan to build a 500-man paramilitary force to combat Cubans and the "support structure" they were implanting in Nicaragua to consolidate the Sandinista regime. Unable to find any Cubans in the jungle, the U.S.-backed commandos, also known as counterrevolutionaries or contras, sought next to interdict arms shipments headed for El Salvador's leftist guerrillas.

When the contras failed in this mission, the administration then recast its goal as one of pressuring the Sandinista government to hold elections and negotiate with its neighbors. Most recently, Reagan has said that the U.S. goal is "to prevent the consolidation of a Soviet-supported communist client state on the mainland of this hemisphere," which, he noted, is "just two days' driving time from Harlingen, Texas."

Even some strong supporters of the contras acknowledged that their poor military performance and lack of a political base inside Nicaragua represent a disappointing return on America's investment, which now exceeds $100 million. Though the contras' military strength is reported at 20,000 men, only a fraction of them are conducting operations inside Nicaragua.

In Angola, the administration belatedly endorsed a drive by conservative political action groups, which had first engineered the repeal of the Clark amendment banning U.S. military aid to Savimbi and then lobbied intensively for military aid to his forces. Not until the fall of 1985 did the president officially embrace Savimbi's struggle. In November, the president approved a two-phased covert CIA operation that would begin providing first intelligence and communications support before graduating to the kind of antiarmor weapons needed by Joao Baptiste against the Soviet-made T62 tank.

Cambodia has remained the lowest-level commitment of the administration and the CIA to any of the anticommunist movements, with CIA nonlethal support estimated at $5 million to $12 million a year.

The realities of U.S. involvement in each of these operations have provoked questions about whether the Reagan doctrine will take on substance and momentum beyond the rhetoric of some presidential aides and speech writers.

"We have no national policy. We have no national strategy," Rep. Earl Hutto (D-Fla.) said recently. "On a national level we are treating all of these conflicts as random events only remotely linked by a vague, generalized ideology from which we are for individual freedoms and against totalitarianism."

Conservatives also hasten to point out the inconsistency in Reagan's embrace of the Nicaraguan contras, Angola's Savimbi and Afghanistan's mujaheddin, while ignoring anticommunist guerrillas fighting in Mozambique and Ethiopia. Indeed, in Mozambique, the Reagan administration is providing economic assistance to the Marxist government in hopes of wooing it away from Moscow.

But one senior administration official said that selectivity reflects case-by-case analysis of how best to pursue U.S. interests; in countries where the United States has become involved in paramilitary operations, the administration is closely supervising them to ensure a continued "political purpose," he added.

This was part of the impetus behind establishing the 208 Committee, to guarantee that the White House and State Department -- and not the CIA -- have ultimate control over this instrument of secret diplomacy.

Some officials feel that such control is badly needed now because of Casey's well-known enthusiasm for covert action. Criticized by his detractors as an inveterate wanderer, Casey is constantly on the move, plotting covert strategy with his station chiefs around the world, inspecting life at the front, interviewing defectors before he briefs Reagan on Soviet intentions. After five years on the job, the director is considered to be in control of his agency now more than ever.

In a few weeks, Robert M. Gates, a Casey favorite, will ascend to the No. 2 post at the CIA in place of McMahon, who was regarded as the "nervous Nellie" of the agency's covert operations.

Gates' first assignment at the CIA in the Reagan era was to whip the analytical arm of the agency into a higher production rate of intelligence estimates on everything from Soviet military trends to Islamic fundamentalism. Most officials believe that Gates will now promote Casey's activist policy for clandestine paramilitary actions with the same zeal.

According to Fortier, the administration's main concern now is proving to the Soviets that the United States has "staying power" in its support of anticommunist resistance groups.

"Staying power is the most essential element," he said, "both in terms of building confidence in the region, but also in terms of demonstrating to the Soviets that cheap solutions are not available, that the problem is going to get worse, that they have to reckon with us."