The State Department expressed admiration and support yesterday for the "incredible story" of rebels in Afghanistan who reportedly have fought Soviet troops to a standstill over the past five years. Officials said there has been no progress toward a negotiated settlement.

In the department's annual observance of the Dec. 27, 1979, Soviet invasion of Afghanistan, Michael Armacost, assistant secretary of state for political affairs, told reporters the United States is "doing what we consider appropriate and necessary" to help the rebels.

He refused to comment on reports that U.S. covert aid has provided the rebels with improved surface-to-air missiles (SAMs) and other arms, noting that the rebels say they capture or buy most of their equipment from Soviet troops.

"But an empirical test of their effectiveness is that they've managed to hold their own and stymie Soviet efforts to advance for the past five years," Armacost said. "If there ever was a true movement for national liberation it is in Afghanistan."

In 1979, Soviet troops overthrew a Marxist government that had been so repressive it was in danger of being overturned by opposition forces. The Soviets then installed Babrak Karmal as president, who invited them in to occupy the country. Now 115,000 Soviet troops control Afghanistan but "may have lost some ground" to the rebels this year, Armacost said.

He said the efforts of neighboring Pakistan to negotiate an agreement "continue to be key" to both the efforts of rebels based there and to U.S. policy calling for a withdrawal of foreign troops. But "the Soviets are not serious" about talking and no progress occurred this year, Armacost said.

Under Babrak's "puppet" government, Armacost said, torture and indiscriminate murder have become commonplace. Rival factions engage in political killings, while the Afghan army is demoralized and undisciplined after suffering an estimated 9,000 casualties. The army has dropped to a third its size five years ago and must use force to obtain recruits, he said.

SAM missiles have brought Soviet aircraft losses to more than 600 in five years, despite a switch to high-altitude bomber flights and the use of flares to divert the missiles, he said.

A major Soviet drive last spring occupied two-thirds of the crucial Panjsher Valley in northeast Afghanistan, near the capital of Kabul, but rebel forces led by Ahmad Shah Mahsud escaped and burned the land behind them in "a classic guerrilla response," Armacost said. "Land mines became the major weapon."

A Soviet siege of Herat in the west ended similarly in June, and since then the rebels have attacked the capital with rockets and given Kabul "the feeling of a city under siege," he continued. The U.S. Embassy there "calls itself Fort Apache," he said.

"There is no reason to believe that the 1984 [Soviet] campaign was any more successful in breaking the strength of the resistance and the support they enjoy than the campaign in 1983," Armacost said.