Washington, April 9. The United States is continuing to ship to Pakistan ammunition and spare parts for weapons under a program begun in 1967.

There is growing evidence that the Pakistani Army has been using American tanks, jet aircraft and other equipment in its attempt to crush the movement for autonomy by the predominantly Bengali citizens in the eastern half of the country.

That equipment was shipped from 1964 to 1966, when the United States embargoed further arms shipments to Pakistan. The embargo was eased in 1967 to permit Pakistan to buy spare parts and ammunition for the weapons.

ESTIMATED AT 30,000

The Pakistani Government forces, estimated at 30,000 to 40,000 men, are believed to have received 48 light tanks and 16 Sabre Jets from the United States before the embargo. They also use British, Soviet and Chinese Communist equipment.

At least twice, the United States has expressed concern to the Pakistanis over reports of the use of American equipment in the east, but otherwise has muted its disapproval for fear of jeopardizing the safe evacuation of Americans from East Pakistan and of appearing to intervene in what the State Department regards as primarily an internal affair.

As the reports have continued, there has been mounting concern in Congress, reflected in the press and in public circles. Four Senators-two Democrats and two Republicans-asked Secretary of State William P. Rogers today to specify United States aid to Pakistan and to clarify whether American weapons had been used by army units against the East Pakistanis.

The Ripon Society, a private organization of progressive young Republicans has made public a study of the Pakistan crisis that urges the Administration to rescind President Nixon's offer of last October to sell arms to Pakistan on a once-only" exception to the 1965 embargo.

The society has also urged that economic aid to Pakistan be suspended and that diplomatic efforts be made to halt the conflict and gain self-determination for the East Pakistanis.

FOUR SENATORS "DEEPLY DISTURBED"

Senator Edmund S. Muskie, Democrat of Maine, Walter ~. Mondale, Democrat of Minnesota Edward Brooke, Republican of Massachusetts, and Mark 0. Hatfield, Republican of Oregon, said in a joint letter that they were "deeply disturbed over the recent bloodshed in East Pakistan." They called on the State Department to disclose "even the most indirect" American involvement.

Congressional sources said that Senators Mondale and Clifford P. Case, Republican of New Jersey, would soon cosponsor a resolution in congress to bar all military aid and sales to Pakistan until the current conflict ended.

From 1954 to 1965 arms aid exceeded $1 billion, according to expert sources here.

Charles W. Bray 3d, State Department spokesman, said that the administration was closely reviewing Pakistani requests for future economic aid-including S20-million in food grains in addition to S87-million for agricultural commodities under an agreement signed last November, United States aid to Pakistan-about S200- million for each of the last two years-makes up 30 percent of all foreign aid reaching Pakistan annually.

CONFERS WITH MCNAMARA

A senior Pakistani finance official, Azi Ali Mohammed, who arrived here two days ago, conferred today with Robert S. McNamara, president of the World Bank, reportedly to request an extension of Pakistan's debt repayment of $20-million due the bank June 30. Mr. McNamara was reported by one informed source to have been "polite-but tough."

Pakistan owes an estimated $4.6-billion to foreign creditors and is facing severe financial difficulties as the conflict with the East continues, experts say. Pakistan's foreign-exchange holdings are reportedly $184-million, and the conflict is said to be costing $70-million monthly. Some United States officials say privately that Pakistan cannot maintain the present expenditures longer than two months.

Meanwhile, there were reports that five lighters, or barges, lying off Chittagong and loaded with United States relief wheat for East Pakistan were fired on today by Pakistani armed forces when they sought to move away. The grain was unloaded in February from two United States-registered ships, the Olympic Power and Olympic Pegasus. Since February the lighters have been stalled off Chittagong, prevented from unloading by Chronic port congestion and the recent disorders.

BURMA EXERTS PRESSURE

Pakistan has reportedly shipped and flown 6,000 to 7,500 men to the East since early March.

In recent days, however, Burma is said to have begun cutting down on vital petroleum supplies both to Pakistan and to Ceylon to bring pressure for a halt to the fighting Pakistani troop planes normally refuel at Colombo, Ceylon. Ceylon has now barred military flights by Pakistan's eight United States-supplied C-130 air transports but is officially overlooking the ferrying of Pakistani troops in civilian clothes on airliners of Pakistan International Airways.

The growing costs in landing rights and fuel charges are, however, said to be worrying Pakistani Government leaders.

"I wouldn't be surprised if the fighting was now costing Pakistan at a rate of $80-million per month," said one official. "That's pretty steep when you realize Pakistan has $4-billion in foreign debts and her reserves are down to $160-million."

EASTERNERS FLEE TOWNS

Goalundo, PAKISTAN, April 9 (AP).-East Pakistanis were reported fleeing towns along the Padma River today, fearing an advance by West Pakistan Army units trying to crush the ,two-week old independence movement in the East.

Women and children in the ferry port of Goalundo and other towns along the Padma the local name for the Ganges River, were said to have started fleeing their homes as soon as word was received that Government troops had occupied the town of Aricha, just across the river.

Local officials ordered residents to take refuge. They said Pakistani Navy gunboats were on their way up the Padma River to cover a crossing by the army.

The inland port of Goalundo would be a logical place for a crossing, because it is at the head of the railway leading from the Padma toward the Indian border, 80 miles west of here.

An army advance along the railway line would stab deep into the heart of territory believed held by East Pakistanis of the Bangla Desh, or Bengal Nation movement.

The East Pakistanis are said to hold most of the territory west of the Padma-Ganges which divides East Pakistan in half. On the other side the West Pakistani Army is reported to control the main urban centers, including Dacca, 40 miles east of the river.