The U.S. Air Force evacuated 61 American Embassy dependents today as the Nicaraguan National Guard repeatedly rocketed the capital's slums, where Sandinista guerrillas fended off ground attacks by government troops.

Several times during the day, the fighting that began in Managua three days ago came within blocks of the headquarters of President Anastasio Somoza and that of the National Guard on which his rule depends.

In the first known desertion from the small but critical Guard air force, a pilot flew his rocket-armed propeller craft to neighboring Costa Rica.

Because intense fighting cut off access to Managua's international airport, the U.S. Embassy mounted an armed convoy to carry the 61 Americans to a private airstrip. A camouflaged C130 turboprop transport, its four motors revving, awaited them. The plane, from the Panama Canal Zone, took the dependents there for transfer to commercial flights going to the United States.

A attempt to pull out the dependents Monday foundered when a Pan American flight bypassed Managua because of the fighting.

Reporters arriving this morning at the offices of the opposition newspaper La Prensa, the scene of heavy street fighting Monday, found the building destroyed.

Neighborhood residents said the newspaper was the target of a direct National Guard tank attack. Its publisher, Pedro Joaquin Chamorro, was assassinated last year after lifelong opposition to the rule of the Somoza family, now in its 43rd year.

The current editor, Chamorro's brother Xavier, said the 15 employes in the plant escaped uninjured when the attack began. The paper ceased publication last week when censorship was imposed under the state of siege.

According to the paper's staff, the Guard troops poured gasoline throughout the building and set it afire after the tank assault.

[The Inter-American Press Association, to which many newspapers of the hemisphere belongs, declared it will not allow La Prensa to die" and will help find facilities elsewhere if necessary until "the Somoza dictatorship comes to an end."]

Fighting in this capital, once confined to well-denied areas, has moved amoeba-like through the capital as guerrillas run down barrio streets, slapping up barricades and waiting for the National Guard to approach them.

With far heavier weapons, more troops and a higher level of training, the National Guard now seems bound to defeat the rebels in Managua. But the Sandinistas, and the barrio youths fighting alongside them, have put up a surprisingly strong battle.

Barring significant Guard defections or a military coup - not seen as likely now - most observers see the current battles ending as those last September, in a Guard victory. But many more will have been killed and seems to doubt that the guerrillas will come again, with support of the citizenry.

While soldiers at garrison headquarters appeared confident and cheerful, those on patrol in the streets are sometimes edgy in the face of what often seem fanatical, near suicidal efforts of the rebels.

In the heavily contested western barrio of Mosignor Lescano this afternoon, National Guard foot patrols and jeeps moved over dirt streets past tin-roofed shacks. As they approached rebel barricades of upturned cars and bricks, they sprayed the trees, where they said the rebels were hiding, with deafening 50-caliber machine-gun and automatic rifle fire.

Patrol leaders said their goal was to drive back the rebels, who are equipped primarily with small-caliber rifles and pistols and gradually clear the streets. Although the guerrillas have some 50-caliber machineguns, the patrol leaders said they were few and usually reserved for the use of trained guerrilla leaders.

In broadcasts today, the government emphatically denied reports on Costa Rican radio that the National Guard air base, and the International airport beside it, had been damaged by guerrilla attacks.

Neither the claim nor the denial could be verified since the road to the airport continued to be blocked by Sandinista baricades and fire fights.

Adding to the unconfirmed rumors of an airport attack was a report that National Guard Capt. Armengol Lara Cruz, who flew his government plane to Costa Rica, had launched two rockets on the landing strip before departing.

The National Guard denied the report. In a communique, the government said Lara Cruz had "stolen" the plane, and that it would ask for its return from Costa Rica.

It is not known whether Lara Cruz intends to offer his services, and those of the rocket-equipped Cessna, to the Sandinistas. As he took off this morning on a supposedly routine mission, he reportedly radioed back asking his fellow pilots on the ground to join him.

The Sandinistas are not known to have any aircraft. Although they claim to have a shot down several government planes in isolated rural areas in recent weeks, the claims remain unconfirmed. Out of an aging air force of Cessnas, C47s and a few T33 jets, the government has acknowledged four recent crashes - all atributed to mechanical or pilot failure.

What the U.S. Embassy called a "voluntary evacuation" of dependents and other U.S. citizens who wanted to leave was shrouded in secrecy to avoid possible guerrilla ambush.

Anti-American feeling has been running high here in recent days, particularly in the barrios. Both rebels and residents verbally assault foreign reporters - all of whom are assumed to be American - charging the United States with supplying the planes and rockets that are attacking their homes.

The evacuation convoy of 13 private and embassy vehicle left Managua accompanied by two small trucks of National Guard soldiers. Embassy officials, saying 80 to 100 of several thousand Americans living in Nicaragua still want to leave, indicated there may be another flight in the next few days.

The em bassy was without electricity today - as are many buildings throughout the city - and operating with only a skeleton staff. Water also has been cut off in large portions of Managua. CAPTION: Picture, Nicaraguans loot National Biscuit Co. plant in Managua as food becomes scarce. UPI