SAN SALVADOR, El Salvador (AP) _ The government's crackdown on the news media has kept Salvadorans in the dark about the most dramatic fighting of the civil war and may even have cost some lives, journalists and others say.

On Nov. 12, the day after leftist rebels launched their biggest offensive of the 10-year-old struggle, the rightist government of President Alfredo Cristiani imposed a state of siege.

The measure suspended rights guaranteed by the constitution, including freedom of expression. Cristiani said Thursday the suspension will last a month.

Since it began, the population has been able to cull only vague or mistaken perceptions of the battles.

In the days after the offensive was launched, all radio and television stations were forced to join the ''cadena nacional'' - the national network. The programming of Radio Cuscatlan, the military station, became the only source of broadcast information and opinion.

Early in the first week of fighting, the cadena dedicated periodic segments to telephone callers, but it screened out leftists.

Several callers denounced the Jesuit priests who ran the Central American University outside San Salvador. They called the priests subversive ideologues and suggested they be expelled or otherwise punished.

On Nov. 16, they were indeed punished.

A group of men broke into the campus residence where six of them were sleeping. They roused the priests, their housekeeper and her 15-year-old daughter and killed them all.

Jesuit authorities say two witnesses saw men in army uniforms enter the house before the killings.

In his homily at the priests' funeral, Arturo Rivera Damas, archbishop of San Salvador, cited ''the climate of hate fostered by the national network'' as a factor in the slayings.

The government has installed censors at all television and radio stations. They make sure viewers and listeners find out only what the government believes strengthens its hand in the fighting.

Predictably, the guerrillas are portrayed as murderous demons, while the armed forces are presented as the epitome of virtue.

In order to downplay the magnitude of the rebel offensive, the simple facts - even where the fighting was taking place - were often withheld.

''The radio says everything is getting back to normal, and everything is under control of the armed forces and the government. But look for yourself,'' said one passer-by in the Soyapango district of the capital late last week.

He pointed down the road.

Fire from assault rifles and machine guns resounded less than a hundred yards away, where several barricaded guerrillas defended an intersection from army troops trying to advance.

Some journalists have publicly made known their objections to the government interference.

On Nov. 22, editors and reporters of the country's principal evening news program - Channel 12's El Dia - stood together before the camera at the show's opening as the anchor read an anti-censorship message. They then signed off indefinitely.

''For ethical reasons, it is impossible for us to continue our broadcasts,'' said a solemn Antonio Mineros. ''We cannot be what we are not.''

Others are willing only to speak privately.

''Because people didn't know what was going on beyond what they could see or hear in their own neighborhood, they didn't know what places were dangerous and what places were safe. The lack of information undoubtedly killed people,'' said a prominent local radio and print newsman who spoke on condition of anonymity.

''A real fear exists that they could kill you for what you say. Even if what you say is not against the government - just for describing objectively what's going on,'' he said.

Some opposition groups have also raised their voices.

''Freedom of expression has been reduced to zero, making it tremendously difficult for the democratic opposition to fulfill its function,'' said the Popular Christian Social Movement in a statement Thursday.