Why is the State Department blocking American aid to Angola? If the "Reagan Doctrine" of supporting freedom fighters in their struggles against pro-Soviet governments applies anywhere, it should apply in Angola, where Jonas Savimbi's troops have waged a long and relatively effective guerrilla war against the Marxist (MPLA) government and Angola's incorporation into the Soviet empire.

Last week the State Department teamed with lobbyists from Gulf/Chevron Oil Co., which has large oil interests in Angola, and with liberal Democrats to defeat in committee a House amendment providing $27 million in assistance to Savimbi's forces and to prevent consideration in the Senate of $50 million in aid.

The House and Senate actions follow congressional repeal last summer of the Clark Amendment, when lawmakers challenged the administration to implement either the "Reagan Doctrine" in Angola or stop talking about it.

"Ideas have consequences," Jack Kemp, a co- sponsor of the House bill, told me last week. "We cannot both proclaim our support for freedom and democracy and refuse to assist people who are fighting against totalitarian government and foreign communist troops."

Yet that is exactly what is happening in Angola, a country of great strategic importance in Africa.

The struggle grows more lopsided each day. Last year more than $2 billion in new military equipment was delivered to Angola to supplement the 1,500 Soviet military personnel, 35,000 Cuban troops and assorted Soviet bloc forces already working to prop up Angola's faltering Marxist government.

MiG fighter jets, attack helicopters, armored personnel carriers and reconnaissance vehicles were provided. It is estimated that 15 percent of the Soviet Union's largest cargo planes were devoted to making these deliveries.

Now a new three-pronged offensive has been launched against Savimbi's forces. It is the first offensive ever attempted during the rainy season, and no one is quite certain how it will turn out. The plan is clear enough: Cuban troops commanded by Soviet officers fresh from Afghanistan hope to split Savimbi's forces, advance on Mavinga and ultimately overrun UNITA's headquarters at Jamba.

Angola's mineral riches, its location vis-a-vis southern and central Africa and its deep water port astride Atlantic sea lanes give that country substantial long-range strategic importance.

Soviet determination to incorporate these assets into the "socialist world system" is clear. Why, then, with UNITA's forces facing heavier, more sophisticated weapons, does the State Department refuse to acknowledge a clear interest in Savimbi's struggle?

Presumably, Assistant Secretary of State Chester Crocker and his associates in the State Department's Africa Bureau still believe they can broker a settlement that will lead to withdrawal of Cuban troops from Angola in exchange for withdrawal of South African troops from Namibia, leaving both countries independent and nonaligned.

Yet after five years of endless trips and conversations, and despite Crocker's considerable diplomatic skill, there is nothing to show for their effort.

The various arguments offered to support the State Department's position have been overwhelmed by the evidence. The number of Cuban, Russian and other Soviet bloc military forces in Angola has increased, not decreased during the last five years. Angolan ties to the Soviet Union have become tighter, not looser. And recent personnel changes have put people with still stronger ties to the U.S.S.R. into key positions.

The MPLA's disdain for the United States hardened as it came to know us better. The Africa Bureau's painstakingly negotiated accord designed to achieve peace in the region broke down completely. And now guerrillas destined for combat in Namibia and South Africa are instructed at a PLO training camp in North Angola. Instead of agreeing to Cuban withdrawal, the MPLA leadership has devised a plan to give Cubans citizenship and presumably the right to remain in Angola forever. Finally, the Soviet Union's direct participation in Angola has increased.

The suggestion that U.S. support for Savimbi will drive the Angolans closer to the Soviets is silly. The MPLA is already fully committed.

The fact that Angola's government has once again agreed to talk with Crocker and his associates provides no grounds for optimism. "The Angolans see negotiations as a stalling operation to stave off aid for UNITA," a western diplomat told The New York Times.

State Department officials should be able to understand that tactic, since they employed a similar stratagem to forestall a congressional decision to provide assistance to UNITA: Confronted with the imminent prospect that Congress would provide substantial overt aid to Savimbi's forces, the State Department recommended token covert assistance that is still not forthcoming.

Yet it is not fair to assign all blame to the State Department. Congress could take the initiative. In the House Rules Committee, it was seven Democrats -- not the State Department -- that blocked action on the Pepper-Kemp Amendment to provide $27 million in aid. In the Senate, Democrats provided most of the votes to prevent the Wallop-Armstrong Amendment for $50 million in assistance from reaching the floor.

Now some senators prefer that no action be taken rather than see passage of a non-binding Senate resolution sponsored by Robert Dole. The resolution threatens steps by Congress if the administration does not act on the Angola situation.

Sen. Malcolm Wallop has asserted he will oppose "a resolution that makes seators feel good for Christmas, but that doesn't do Savimbi one damn bit of good."

Many in both houses feel that a bill providing aid for Savimbi's forces would pass in either chamber if it could be brought to a vote.

Perhaps. In any case, Americans will have the opportunity to reflect during the holiday season on the odd behavior of a government that proposes more than $15 billion in overall foreign assistance, but nothing for Savimbi's struggle in which our principles and our interests are so clearly engaged.