Holden Roberto, the Angolan guerrilla leader whom the Reagan Doctrine has bypassed so far, returned to Washington yesterday to appeal for some of the covert military assistance that the United States is channeling to Jonas Savimbi's rival UNITA faction.

Roberto's FNLA faction was the prime beneficiary of CIA support during the Angolan civil war in 1975, but it has since fallen on hard times and Roberto now lives in exile in a Paris suburb. His visit to Washington yesterday contrasted sharply with Savimbi's triumphant tour in February, when -- aided by a $600,000 public relations contract with a politically active firm here -- Savimbi was embraced by President Reagan and many conservative leaders.

At the White House yesterday, a National Security Council staff member declined to meet with Roberto. "Recently, we haven't had official contact with that organization," an administration official said.

But Roberto, speaking before a Capitol Hill panel that ranged from zero to three Republican congressmen in attendance, argued that as the Reagan administration extends aid to guerrillas fighting Marxist governments around the world, his party should be included.

To rebut charges that his FNLA is moribund, Roberto produced his field commander, 38-year-old Alberto Vilela, who in turn removed his shirt to show the scars of war.

"The FNLA is not dead, but it is silent because it lacks the means to create a vigorous and costly public relations campaign," Roberto said in his testimony at a hearing chaired by Rep. James A. Courter (R-N.J.). "It would also be undemocratic if one particular political movement were to be designated in advance as the sole representative of the free Angolan people."

UNITA (National Union for the Total Independence of Angola) and the FNLA (National Front for the Liberation of Angola) lost a three-way civil war a decade ago in the southern African country of Angola, until then a Portuguese colony. The winning party, the MPLA (Popular Movement for the Liberation of Angola), captured control of the capital and oil fields and has been supported ever since by thousands of Cuban troops.

UNITA, which originally had China's support, has received substantial backing from South Africa and never stopped fighting in southern Angola. But the FNLA, which had been supported by Israel and the United States, withered in the field when those backers and Zaire, Angola's northern neighbor, withdrew support in the mid-1970s.

The challenge facing Roberto in his quest for funds and weapons was evident in the fact that the Republican Study Committee, which sponsored yesterday's hearing, also distributed a paper that calls UNITA "the only effective resistance movement battling the communist" Angolan government. An administration official said that Roberto, although pro-Western and an admirable man, has not been an effective leader and no longer commands a viable force.

Vilela, who said he is inspector general of Roberto's army, agreed that his troops are woefully underequipped, but said he still has 5,000 men in the field. Some have no weapons, he said, and those that have weapons frequently have little or no ammunition -- "two bullets apiece," as Roberto said.

The slightly built Vilela, with a blond mustache and wearing a denim jacket and gray slacks, also said that his men are hard-pressed because they cannot retreat into Zaire or other neighboring countries. He said he walked for a month and a half from his headquarters in the northern Angolan bush to a city, which he did not name, from where he could fly out of the region.

Vilela and Roberto had not seen each other since 1979, Vilela added, when the FNLA founder and president last visited Angola.

But Vilela also said that the FNLA has the support of 100,000 people in four provinces and, with U.S. assistance, could field an army of 15,000 to 18,000 soldiers.

"We are hoping -- and that's why I am here -- that we have the same right to help as anyone else," he said. "I am trying to find out if it is the intention of the United States to sell us out."