Sandinista guerrilla barricades again cut off the route to the international airport here today as fighting continused in outlying areas of the city.

Refugee centers around the country in which an estimated 150,000 have sought shelter from street battles and National Guard air attacks are quickly running out of food, relief officials said.

They said that at least 50,000 of the refugees were in Managua, where the National Guard has been battling guerrillas in poor barrios all this week, Managua's population is 500,000.

The officials said that medical supplies were still adequate. Yet one American doctor working in Managua's largest children's hospital said at least 25 cases of polio had been brought there in the past few weeks. He classified the outbreak as an epidemic.

The military hospital here has asked the International Red Cross to supply several thousand dollars worth of medicine.

There is no way to estimate the number killed or wounded in the most fiercely contested areas of Managua and other parts of the country, since Red Cross ambulances have been unable to enter them.

The guerrillas, who have stockpiled medical supplies for a long time, have set up their own clinics within the areas they control. Military wounded are taken to National Guard hospitals.

Meanwhile, the U.S. Air Force evacuated another group of American citizens from Nicaragua today. The C130 transport touched down briefly to get the passengers at President Anastasio Somoza's private airstrip at Montelimar, his beachside home 40 miles northwest of here. The 70 departing Americans were accompanied by a score of people from other countries.

For the second time in the past two weeks, rumors circulated througout the city that at least two of Somoza's Cabinet ministers tried to leave the country on the one commercial flight that landed here today, and were arrested at the airport. Somoza denied the rumors.

Looting by Nicaraguans from the poor barrios of the capital spread today to Managua's largest shopping centers in the southern part of the city. Thousands coverged on the centers on foot and in vehicles. They piled pickup trucks with beds and bicycles.

Ragged children ran gleefully through the carnage, their arms full of toys, as some people shouted in vain to their fellow looters to pick up only food and not waste their time with other goods.

In the far northwestern part of the city, past the rebel barricades that reach almost to the airport, another crowd broke into a large chicken farm and carried off thousands of brids. That raises the possibility that eggs, which have been relatively plentiful, will also become scarce.

The guerrillas ambushed at least two National Guard patrols this morning, one just outside Managua on the southern highway. The guard claimed it had killed more than 30 rebels in fending off the attach and had suffered only three wounded. Reporters arriving on the scene found only six Sandinista bodies.

On the northern highway, five miles south of Leon, a group of about 24 guardsmen was ambushed but managed to drive off the guerrillas and kill one. His body, the top of the head completely blown off, was thrown in the back of a pickup truck and carried back to Managua.

Leon, which has been largely under guerrilla control for nearly two weeks, was subjected to heavy air attach throughout the day. Military officials said the objective was to stop the guerrillas' major push, launched Wednesday, against Leon's military garrison.

Until now garrison snipers have successfully prevented the rebels from getting any closer than within a few blocks.

In a small housing development just outside the city today, a professor of ecology said his family has been without electricity for nearly two weeks now. Like many others, however, he had stored supplies of food in anticipation of the fighting.

Offering a warm Coca Cola, the professor showed off a bomb shelter he has built of sandbags and bricks in his backyard.

As he spoke, two Guard Cessnas and a helicopter gunship flew low overhead firing rockets into the city half a mile away.

The professor said most of his students had joined the Sandinistas. Himself a Social Democrat, the professor said he believed that Sandinistas were willing to let a moderate civilian government replace Somoza and not planning to take control themselves.

Rubbing his scraggly chin, the professor said he had devided "not to shave until Somoza is gone. Some people have told me I am going to trip over my own beard before that day comes."

[In Washington, Rep. Thomas R. Harkin (D-Iowa) called for a ban on the approximately 65 million pounds of beef that Nicaragua exports to the United States annually, Harkin, a prominent congressional exponent of an activist human rights policy, charged in a speech to the House that Somoza and his friends control almost three-quarters of the $100-million-a-year, beef-export business.] CAPTION: Picture, Managua residents loot a market damaged in battles between rebels and troops. UPI