SAMARKHEL, AFGHANISTAN, JULY 7 -- The Afghan government has won an important victory over mujaheddin guerrillas, breaking their siege of Jalalabad and taking the initiative with its own forces for the first time since Soviet troops withdrew from the country in February. To demonstrate their victory, government officials brought journalists to this village seven miles east of Jalalabad, which until this week had been a key military garrison held by the mujaheddin resistance fighters. Government troops halted their three-day advance today and worked to consolidate their positions. However, senior military officers, including the governor of Ningrahar province, vowed the offensive would continue in an effort to drive guerrillas in the province eastward to the Pakistani border. Government control in eastern Ningrahar collapsed rapidly last winter when Afghan army units defected or fled as the Soviet troops, who had been backing them up, withdrew. At the time, U.S. government analysts cited the Afghan government collapse in this province as a sign that the guerrillas could defeat the government within six to 12 months. The government's success here this week undermines mujaheddin hopes for a quick victory. It also is a setback to the U.S.-Pakistani policy that supports the guerrillas in their fight against the Kabul government of President Najibullah. While the government's advance allows it to approach a key guerrilla defense line east of Jalalabad, the major impact of the battle on both sides is likely to be psychological, said analysts in Kabul and Pakistan. A central element in the government's original loss of eastern Ningrahar to the rebels was poor morale in the army. That clearly has changed with the latest victories. Government soldiers here and in Jalalabad were ebullient today, laughing and raising their arms in victory as the bus carrying foreign journalists passed. While the internal politics of the ruling People's Democratic Party are shrouded, one analyst in Kabul suggested that the victory will strengthen Najibullah against hard-liners who appear to have reservations about his offers to negotiate peace with the mujaheddin. The government kept up a barrage of artillery fire from positions in and around Jalalabad today but conducted none of the air strikes that it used to cover its advances earlier this week. Tanks moved back and forth on the paved road between the front line and Jalalabad, but there was no major movement of armor or troops that suggested an immediate new push. While government troops clearly face no further major resistance at Samarkhel, there was evidence that they are continuing to encounter small groups of mujaheddin. Officials brought reporters to the western edge of the village but refused to take them to the military base here that is a key stronghold along the paved road to the Khyber Pass and Pakistan. On a steep, rocky mountain that dominates Samarkhel, government soldiers crept up a ridge while a tank at the base of the mountain fired shells farther up the ridge. During the operation, a few bursts of automatic rifle fire were heard. The governor of Ningrahar province, Lt. Gen. Manoky Mangal, said his forces had killed more than 2,000 guerrillas during fighting Tuesday and Wednesday, while suffering only 23 dead or wounded. He would not say when the government might resume its offensive but expressed confidence that its victories of the past three days foretell a successful sweep to the Pakistani border. The government and mujaheddin are ranged along a north-south front just east of here. The mujaheddin apparently are holding a ridge that offers them their only natural defense line for many miles. It was not immediately clear why the government offensive has succeeded thus far, although it may be that the effort simply caught the mujaheddin by surprise. Foreign residents of Kabul said that the government has not fought so hard, with heavy air and missile strikes, since the March guerrilla offensive at Jalalabad, when the government was in a defensive position. The government apparently was well prepared for its attack. Maj. Gen. Abdul Khalek, commander of tank forces in the offensive, said units from Kabul were brought to the Jalalabad area a week ago. Western analysts of the war have noted that a major guerrilla weakness in the Jalalabad battle was their failure to close the road supplying Jalalabad from Kabul. Another factor in the mujaheddin's defeat may be the continued fractiousness of the guerrillas' seven, Pakistan-based political leaders, who have made no progress in unifying or broadening their alternative government. Also, diplomatic sources in Kabul and Pakistan have said arms deliveries to the mujaheddin via Pakistan inexplicably have slowed recently. Today, the smell of smoke lingered in Samarkhel from trees and buildings burned in the fighting. At a government-built compound for workers in an olive oil plant, houses stood roofless, some with their walls collapsed. Mujaheddin weapons were piled outside a house: Soviet-made artillery shells, Soviet hand-grenades, still packed like eggs in boxes, and Chinese rocket-propelled grenades. Nearby, other factories and a two-story generating station stood ruined. One stone wall of the station was blasted away, and its diesel turbines were half-buried in rubble. The station's fuel-oil storage tanks were not damaged. The station's outbuildings had been rifled and Islamic fundamentalist slogans daubed on the walls. "Death to the infidels of the world," one slogan read. It was difficult to tell how much of the damage had been caused in this week's offensive and how much by the guerrillas' capture of Samarkhel last March. The visit to Jalalabad was tightly controlled, with journalists prohibited from speaking independently to local residents. But residents' declarations of relief at being out from under the daily barrage of missiles appeared genuine. "Life has been very frightening here. You never knew when something might fall and kill you or the person next to you," said Guljan Muhammed, a shopkeeper in the center of town. While only the Jalalabad airport appeared devastated by the weeks of missile attacks, the evidence of missile or shell explosions was everywhere in the city. Hundreds of craters in walls and streets indicated explosions of relatively small missiles, not powerful enough to destroy buildings, but sufficient to kill within a radius of perhaps 10 yards. Although today's visit to Jalalabad demonstrated that the government has pushed the guerrillas several miles away from the city, it also underscored Kabul's inability to control the rugged terrain outside the city. The Afghan air force helicopter that flew journalists between Kabul and Jalalabad was escorted by four other helicopters, including three heavily armed Mi-24 gunships. For much of the trip, the helicopters wove along mountain valleys, rising just high enough to fly over steep ridges before dropping down into the next valley. The helicopters fired flares to ward off heat-seeking missiles, such as the U.S.-made Stinger, and several times, the pilot of the journalists' craft fired rockets at suspected guerrilla hiding places. The mujheddin threat to government air traffic in eastern Afghanistan was underlined by the burned and shattered wreckage of five helicopters along the route.