They call it "liberated Leon," the first city to be conquered and controlled by Sandinista guerrillas after the fall of the government's military garrison here over the weekend.

But while the streets of Leon belong to the guerillas, who wander easily with rifles slung over their shoulders, the skies still belong to the President Anastasio Somoza.

Last night, as the Sandinistas in Leon enjoyed a brief celebration after Somoza's planes stopped their attacks at dark, the president insisted during an interview in his fortified "bunker" in Managua that he still has the support of most Nicaraguans.

While he acknowledge that his chances of remaining in power have lessened in recent weeks. Somoza said he would go down fighting against the Sandinista-led revolution. "They'll have to throw me out," he said.

Gen. Somoza was dressed in combat fatigues, with his name sewn over the pocket. Behind him on the walls of the meeting room hung aerial photos of Nicaraguan cities with target areas circled.

Three weeks ago, the Sandinista National Liberation Front launched what it called a final offensive against Somoza's government.So far, the guerrillas have managed to "occupy" portions of a number of northern Nicaraguan cities, with their principal strength here in Leon.

Many government ground troops in the north have been withdrawn to fight in Managua and in the south, where the government is battling a 700-strong guerrilla column that invaded over the Costa Rican border last weekend.

Despite guerrilla gains on the ground, however, the National Guard appears to have an inexhaustible supply of rockets and artillery rounds that theoretically could keep the Sandinistas at bay indefinitely.

Some human right organizations and foreign governments have charged Somoza with genocide. There is little doubt that civillian casualities are high and that much of Nicaragua is being destroyed in his attempt to retain the power his family has held here for 46 years.

Last night, the normally effusive and aggressive president appeared agitated and worried, shifting impatiently in his chair and tugging on a gold medallion around his neck.

His dark, air-conditioned office complex has turned into an armed camp. Combat-equipped soldiers stand behind sandbag fortifications at its entrance. Inside, heavy-booted soldiers pass by with sidearms tucked in their belts or holsters.

The Cabinet now meets twice daily, but most of the ministers long ago sent their families out of Nicaragua to safety and now sleep in the bunker, or in the well guarded hotel across the street.

Armed government security agents in plain clothes, who roam the hotel lobby by day, gather in the bar at night and there is a sense of impending doom in their heavy drinking and too-loud laughter.

Still, Somoza has appeared to relish the military aspect of the struggle. He had served as commanding general of the National Guard under the presidency of his brother Luis, and seems most confortable in the company of plain-spoken military men.

In fiery speeches, he has consistently portrayed the civil war here as a military problem. He has denounced international communist "offensive" against his government and portrayed himself as the front line against a communist takeover in the hemisphere.

Few Latin American governments publicly disagreed with him until recently. Now, some of the other countries in whose name he is fighting have begun to desert him.

Over the weekend, four ostensibly neutral South American governments, along with long time Somoza foe Venezuela, released a statement indicating they were prepared eventually to recognize a provisional Sandinista government.

One of those countries, Ecuador, broke relations with Nicaragua. Somoza said he expected the others, including Columbia, Bolivia, Peru and Venezuela, to follow suit. Mexico and Costa Rica have already severed diplomatic ties with his government.

[Last night, Panamanian President Aristides Royo announced that Panama, too, has severed diplomatic ties to Nicaragua.]

Somoza, commenting on the Sandinista hope to establish a provisional capital in the southeren city of Rivas, warned: "If they get some sizable part of the territory, they might get recognition" by other governments. "Then you wil have war in the Americas."

That war will come, Somoza said, "even if I stay with one friend, myself."

While Somoza said he felt "very bad" about the widespread destruction in the capital, he attributed much of it to civilian looting. "We see people in the streets . . . We haven't shot at them. But do they come against Somoza? No, they come against the capitalists," he said.

Referring to widespread opposition to his government among business leaders, who have now fled with their families, Somoza, a West Point graduate, declared: "I'm still the storekeeper for those sons of bitches who left the country with their money. They expect me to watch over their goods? Baloney."

Somoza charged the United States with pressuring other governments in the hemisphere to turn against him, and with confusing "freedom" with anarchy.

While he claimed the support of "most Nicarauguans," few in Leon today had a kind word to say for Somoza.

Movement by both guerrillas and civilians in Leon is in well-timed spurts, between the .50 caliber bursts and rockets fired from two planes that droned overhead throughout the day.

Even small children know that the dip of the wings means the plane is about the fire, and the youngsters quickly pull each other under cover.

Pointing into the sky, and toward a National Guard fortress several miles away from which mortar rounds were being fired on the city, Leon residents spoke of terror and tyranny. Some groused about Sandinista incomptency in distributing food in the city, but the vast majority said they were with "the boys."

While the Sandinistas handled the military situation, noncombatant guerrilla sympathizers divided the city into zones. Block groups take daily census and distribute food and propaganda. Each zone also has a Sandinista military post in a house or office within its limits.

In a makeshift hospital stafed by student doctors in one zone, a dozen wounded and previously bandaged children waited for attention. Behind the clinic, in a small room, guerrillas showed reporters four wounded National Guardsmen they had taken prisoner.

Although the Sandinista consider the garrison fallen, a half dozen National Guardsmen remain inside, sniping at all who pass through the center of town. Much of the garrison's ammunition and at least one armoured vehicle have been captured by the gerrillas who proudly showed off their prizes after removing camoflage covers of leaves and branches. CAPTION: Picture, Sandinistas guard Nicaraguan troops captured in Leon while trying to escape by removing their uniforms and blending with the civilians as guerrillas took over.