BANGKOK, March 29.-The universal attitude expressed in Dacca by representative Bengalis from Sheikh Mujibur Rahman down to the street vendor is that the United States has wittingly or otherwise made it possible for West Pakistan to ride roughshod over the East through its military assistance to Punjabi-dominated army and an economic aid approach reflecting the bias of largely West Pakistani bureaucracy.

Prominent Bengalis such as the late Premier H. S. Suhrawardy warned privately when the United States started its military aid in the 50s that it would ultimately be used to suppress Bengali aspirations. The army wanted American firepower, he once said, more for domestic political reasons and for use against the Indians than for the stated purpose of countering international Communism. But even Suhrawardy never anticipated the carnage inflicted on Thursday night by M24 "chaffee" tanks provided under the now defunct military aid program.

Despite the marginal supplies of Chinese and Soviet military equipment supplied since the United States terminated its grant military aid in 1965, Bengalis stress that the army is still overwhelmingly American oriented and point to the recent controversial decision by the Nixon administration to sell a small amount of equipment and spare parts to Rawalpindi for the first time since the Indo-Pakistan war. Every time one of the giant U.S. C-130 transport planes with troop reinforcements zoomed overhead in Dacca last week, Bengalis made acid comments for the benefit of Americans present.

One of the key advisers to Sheikh Mujibur Rahman said that Awami League leaders see a U.S. hand behind the hawkish counsel given to Yahya in Dacca by Gen. U. A. Umar, secretary of the National Security Council, and Gen. Mohammad Akbar, director of Inter Service Intelligence.

Generals Umar and Akbar are regarded in the Awami League as Islamic zealots who pushed Yahya into his military confrontation on Thursday, and "some sections" of the U.S. establishment in Pakistan with old ties dating back to the days of the military alliance are blamed, in turn, for allegedly encouraging the hardliners.

Conversations with Awami League leaders, key West Pakistanis and American sources suggest that the attitude of U.S. Ambassador Joseph Farland in his formal contacts with ,both West Pakistani and Bengali leaders has been one of reticence and detachment.

But in the Bengali view, this amounted to giving Yahya a blank check, and the United States should at least have made a serious and explicit effort to prevent the use of American military hardware against East Pakistan,

When Yahya asked him in a late February meeting what he should do, Farland reportedly stuck to his script and replied that the United States would honor "whatever the people of Pakistan decide." Farland also met the Sheikh two days before Yahya made his March 3 speech postponing a scheduled constitution-drafting session of the National Assembly. He reportedly sounded out the Sheikh on key foreign policy issues and heard him out on Bengali grievances but said little.

It is understood that the Sheikh asked the United States to observe "genuine" impartiality if it did not wish to take sides and to avoid getting into the position of indirectly underwriting whatever West Pakistan chose to do. He emphasized the need for restraint by the army, and reiterated his often-stated differences with Yahya's foreign policy, warning of future Chinese pressures and underlining the advantages for East Pakistan in trade with Indian West Bengal.

He spoke proudly of the overwhelming election mandate won by the Awami League. This provided the necessary moderate democratic political base on which to build the state economically, he contended, warning that revolutionary forces of varying stripes were lying in readiness to exploit his failure.

The underlying tone of Bengali comments concerning the role of the United States has been one of distress rather than anger at a time when the United States is still viewed as the only conceivable source of salvation for East Pakistan. One common theme is that the United States has been "egocentrically" thinking of its own foreign policy interests in a narrow way without regard for Bengali aspirations.

Thus, it is argued, the United States has been hoping for a relatively strong central government with the Sheikh as premier, since the Sheikh's views on China would presumably have shifted Pakistani foreign policy in a westerly direction. The Bengalis, however, do not want the Sheikh to go to Rawalpindi. They want loose confederation with a token central authority, and the United States, in this view, has indirectly encouraged Yahya in his hard line.

Another factor often cited as evidence of U S. bias toward the west wing is the identification of U.S. aid officials and the World Bank with the thinking of West Pakistani economic planners. Bengali economists believe that the planners in Rawalpindi led by M. M, Ahmed, Yahya's principal economic adviser, are frankly dedicated to maintaining "neo colonial' relationship between East and West Pakistan in which Bengal serves as more or less permanent golden market for West Pakistani industry, market protected from foreign competition by tariffs in which prices can be jacked up at the will of West Pakistani entrepreneurs.

The Bengali nationalist weekly "Forum" cites the report of 1970 U.S. aid report on industrialization in East Pakistan and recent World Bank staff study as reflecting the Rawalpindi attitude. Both studies urged tax incentives for West Pakistani investors and implied that there is no entrepreneurial talent in the East.

The banks resident director in Pakistan, David Gordon, grants ,that there might have been "some insensitivity" to Bengali needs on the part of Western aid officials in the past reflecting close working ties with Rawalpindi officials.

But Bengali experts have recently begun to come up with clear, well-planned projects, and the bank's Pakistan aid consortium has been shifting its major interest during the past year from the western wing to the east "In the belief that this is where the problems are." Gordon arrived in Dacca last Thursday afternoon with hopes that a political settlement might be in the offing and discussed future aid possibilities amid the background music or mortars and cannon.

One of his tasks had been to confer with local officials on priorities governing a long-term $1.6 billion flood control program for East Pakistan adopted by the bank last summer. The aid givers have "positive attitude," he observed with a glance at a tank visible through the hotel window, and more than $125 million has already been pledged, "but perhaps the pertinent question is will we have any government, administration or economy to deal with about floods or anything else."