MYMENSINGH, Pakistan.-From a helicopter flying over the eastern region of East Pakistan, vast destruction could be seen in towns and villages but no evidence of continuing fighting.

There is virtually no battle damage, however, in the city of Mymensingh, which was captured by Government soldiers from separatist Bengali troops in a one-day battle April 16. But a visit here is a visit to a city of desolation,

Apart from a handful of people at the market place, who carefully saluted passing army jeeps, the city was virtually deserted.

GRAVES IN THE STREETS

At intervals along streets lined with ramshackle houses bodies have been buried in shallow graves and covered with piles of red bricks. Bodies covered with bricks are found even on the porches of houses, which themselves are unoccupied and closed.

Authorities said that of a heavily armed Bengali insurgent group of about 1,000, nearly all had been killed in the fighting. The insurgents were said to have been well entrenched and armed with anti-aircraft machine guns, mortars and rocket launchers, largely of Indian origin.

Officials also said that, before the Government soldiers took the city, the Bengalis had killed at least 1,000 Bihari or non-Bengali residents. Army officials introduced correspondents to people who said there had been a slaughter of Bihari residents by the dominant Bengali group led by members of the Awami League, the political party that was outlawed by the central Government soon after the military action began in East Pakistan on March 26.

("There were 6,000 non-Bengalis where I lived and now there are 26 survivors," the Associated Press quoted the assistant postmaster as having said.)

Officers from West Pakistan commanding the forces occupying this region decline to disclose overall casualty figures in Mymensingh District, which is described as the most populous single district in all south Asia. Such figures, in any case, may not be known.

"There were so many bodies here," one officer said, "It was impossible to identify them or bury them."

He said they had to be thrown into the Brahmaputra River, a tributary of the Ganges. For the last two months, it is said, swarms of vultures have been gathering in the area.

The main loss of life here apparently occurred in the fields and fruit groves outside Mymensingh, and in clusters of huts that had been burned to the ground.

In Dacca, capital of East Pakistan, corespondents were shown three prisoners said to have been captured from the ranks of infiltrating Indian forces inside Pakistan.

Army Controls Towns

The three men said that they had been sent to Indian border posts and had removed their unit badges before crossing the frontier. Pakistani authorities said that they had captured five Indian border guards in all, one of them wounded.

There seems little question at this point that the army is in full control of all major towns of East Pakistan, most of which have been evacuated by at least half the residents.

Army officials said that pockets of resistance continue. They said that attempts had been made to blow up bridges and other lines of communication but that search-and- destroy operations with helicopter support were rapidly neutralizing these.