The Salvadoran government apparently has completed what was reported to be a major offensive against guerrillas dug in around this provincial capital 75 miles east of San Salvador.

About 1,200 government soldiers were seen leaving the area yesterday in long truck convoys. Roads that had been blocked since Friday, with military guards warning of a major action against guerrilla camps and supply depots in the area east and south of here, were opened again.

The colonel in command of the Usulutan district later told an ABC television crew that 28 guerrillas had been killed in the operation.

"We have cleared the entire area. There are no terrorists left here," he said.

Local newspapers quoted unnamed military sources as saying the operation, in a region where the government previously had estimated the guerrilla population at 1,000, was a complete success, with "many" guerrilla casualties.

The clandestine guerrilla Radio Venceremos, however, said the entire operation had been a failure.

A visit to the region left a number of questions as to what happened here, if anything. No wounded were visible among the truckloads of soldiers, who all appeared trimly dressed and cheerful. As they passed through town, cheering citizens threw them fruit, candy and cigarettes.

A woman who tossed candy into the troop trucks said she had done so because "they are good boys and they are tired."

Another woman said she was relieved that the episode had ended.

"It's so hard to lead a normal life," she said. "You have to be careful all the time whom you talk to. I speak now only to people I know. It makes everybody very suspicious."

A third woman said she had seen some soldiers questioning two women carrying guns, "so they had to be guerrillas." She said that one woman was about six months pregnant. "She was carrying her machine gun and her stomach, nothing else," the woman said.

Diplomatic observers speculated that heavy publicity on the military buildup here last weekend had given the main guerrilla forces time to leave before the assault began Sunday evening. But in the area around Jucuaran where the fighting was said to have been heavy, peasants at Hacienda la Cabana said they had heard only sporadic gunfire.

By contrast, newspapers were full of pictures today of burned-out buses and buildings in the town of Apopa, a half hour's drive north of the capital, where guerrillas armed with bazookas attacked early yesterday morning.

The guerrillas reportedly bombed the town hall, destroying all the Civil Registry documents that include proofs of residence required for voting. The guerrillas have denounced elections scheduled March 28 as a farce and have destroyed registry papers in several towns during the past month.

Newspaper reports said two National Guardsmen were killed and nine people were wounded, including four civilians.

A CBS network television crew obtained pictures yesterday of soldiers burning the bodies of several guerrillas following weekend fighting around San Sebastian, northeast of San Salvador. One soldier cut off the head of a guerrilla's corpse and held it up for the cameras.

A CBS spokesman in New York said no such film was shown on any of the network's news shows.

No one claimed to have counted either the number of attackers or the number of casualties on either side, and reporters saw only five bodies, all apparently guerrillas.