For a man who has been killed twice in the past seven months, Ahmed Shah Massoud is in remarkably good health.

Despite Radio Afghanistan announcements of his death in two major Soviet offensives this year, the 31-year-old resistance commander of Afghanistan's Panjshir Valley is well, confident of his forces' ability to push back Soviet-backed government troops, and -- surprisingly -- shows no signs of strain under continuous battlefield pressures.

In conversations during an 18-day period in the Panjshir, Massoud expressed appreciation for the Kabul government's repeated announcements of the complete defeat of the guerrillas, known as mujaheddin, and his own death.

"Every time they proclaim our defeat and a month later are themselves taking heavy casualties again, our reputation increases," he said. "We should thank them for this."

The reputation of Panjshir's rebels and of Massoud has grown steadily since the Soviet invasion of this country in December 1979. Estimated at between 5,000 and 10,000 insurgents, his men have repulsed eight large-scale Soviet and Afghan Army assaults on this strategic valley northeast of Kabul.

At the same time, Panjshir guerrillas, organized into small, mobile groups, have disrupted communications along the single highway north to the Soviet border and carried out operations increasingly far from the Panjshir in coordination with other resistance groups.

Soviet and Afghan authorities have been frustrated by, and determined to destroy, a man generally recognized as one of the resistance's most astute commanders. The son of a retired Army officer and a former student at Kabul's Soviet Polytechnic, Massoud has displayed a grasp of modern guerrilla warfare that sets him apart from typically tradition-oriented mujaheddin chiefs.

Early this year, Afghanistan's secret police, Khad, moved with backing from its Soviet counterpart, the KGB, to eliminate Massoud. The assassination was to have taken place in April on the eve of a massive ground and air blitz against the valley. But the plan backfired badly. At the eleventh hour, it became clear that the handpicked assassin, a longtime acquaintance of Massoud's being paid by Khad, had, for years, been a double agent working with the Panjshir resistance.

More recent efforts to kill Massoud have relied on air strikes on villages where he was suspected to be operating. In late September, Soviet jets, apparently acting on intelligence reports, bombed a house within 50 yards of his temporary base.

Basic precautions have minimized the chance of a hit, however. Constantly on the move between rebel bases in the valley, Massoud is seldom in one location for more than a few hours.

When he does establish a temporary command post in a cave or bombed-out house, his time is spent reading military and intelligence reports, issuing written orders and discussing the situation with local commanders. Among men not generally given to unquestioning obedience, his authority is quiet and total.

For Massoud and his staff, who move frequently without warning, and often at night, probably the only routine is set by prayer five times a day and tuning in to news reports from Radio Afghanistan and the Persian-language services of the British Broadcasting Corp. and Voice of America on a pocket-sized shortwave transistor.

An intense man with evident intellectual curiosity and a wry sense of humor, Panjshir's young commander appears to relax only occasionally, usually over a game of chess. But he reveals a voracious interest in national and international affairs and questions visitors closely on the political complexities of western government.

Massoud's interest in the West focused primarily on the issue of support for the Afghan resistance. He expressed disappointment over the lack of outside aid reaching his front.

Given the intensity of Soviet operations against the valley, supplies reaching the Panjshir were hardly sufficient for effective defense, let alone more aggressive offensive strikes and an effective coordination of resistance fronts, he said.

He ridiculed one western press report of an elaborate supply pipeline to the Panjshir masterminded by the CIA. According to the report, the CIA was supplying Massoud with surface-to-air missiles, satellite intelligence, radio transmitters and conventional military hardware.

Massoud and his staff were particularly amused by suggestions in the report of occasional CIA-organized airdrops of supplies. Munitions this correspondent saw coming into the Panjshir were brought in on horseback over rugged mountain terrain. Aircraft over the valley were in abundance, but all appeared to be Soviet, and most were dropping bombs.

It is difficult to determine either the origin or the source of financing of munitions arriving here. Weapons, including rocket launchers, heavy machine guns and recoilless rifles, were all of Soviet Bloc design. Most ammunition appeared to be of Chinese manufacture.

Massoud insisted that most of the weaponry and ammunition used by his forces had been captured from Soviet and Afghan troops.

With the exception of some Chinese-manufactured type 56-1 assault rifles, rebels here were armed largely with Soviet-manufactured AKM and new AK47 automatic rifles. Some rebels also carried the latest Soviet "Krinkov" 5.45-mm submachine guns.

Low-flying Soviet jets were seen in the Panjshir being engaged by heavy rebel machine-gun fire from mountaintop positions. But ground-to-air missiles never were used.