The major aid-giving nations, led by the World Bank, have quietly agreed to postpone indefinitely any new economic assistance for Pakistan.

A consensus of the 11 donors was reached at a meeting on Monday in Paris, it was learned yesterday. The informal decision was taken after a mission from the World Bank and International Monetary Fund reported after a visit that Pakistan was an administrative and economic shambles.

The agreement will not affect the humanitarian assistance that nations intend to give Pakistan or its refugees in India. It does, however, hold up several hundred million dollars in development funds on which President Yahya Khan's regime had been counting.

In the last year in which normal aid flowed, the budget year ending June 30, 1970, Pakistan received $316 million from the donors.

In addition, it was learned, the IMF has decided for now against giving the central government a $250 million package of foreign exchange that the Fund had been considering.

The Paris consensus was reached with the assent of the United States, despite strong urgings to the contrary from some U.S. quarters. Washington's ambassador to Pakistan, Joseph S. Farland, is known to believe the donor nations should meet soon to pledge assistance to greater influence the central government and lessen its dependence on China.

But the Paris meeting concluded that no early gathering of the aid consortium should be held because it would openly confirm the widespread opposition to assistance now.

According to reliable sources, Belgium, Canada and Britain argued strongly in Paris that public opinion in their countries deeply opposes aid to Pakistan and that none should be forthcoming until Yahya's regime reestablished civilian rule in East Pakistan.

Yahya is expected to pledge on Monday the eventual restoration Of civilian government in East Pakistan. But knowledgeable officials are predicting that his promise will be hedged with too many qualifications to be taken seriously.

The 11 nations at Paris - the others were Japan, Norway, the Netherlands, Prance, Germany, Italy and Denmark, with Sweden as an observer - were strongly influenced by a devastating report from Peter Cargill; he is director of the World Bank's South Asia department, chairman of the Pakistan aid consortium, and has just led a Bank- Fund team to Pakistan.

Cargill and the other team members were permitted by the central government to travel freely through East Pakistan during the first two and a half weeks in June. According to those familiar with Cargill's report, the mission found:

A continuing reign of terror in East Pakistan conducted by the 70,000 West Pakistani troops there. The army had been given a free hand to deal with "secessionists." And Hindu or Awami League member is said to fall under this heading.

One team member was told of 50 Hindus who had been slaughtered and their corpses pushed into a river the day before his arrival in a town. A driver led him to two corpses whose submersion was incomplete.

The shattering of urban life. The mission found towns with only 10 per cent of the population remaining. The rest had been killed, had dispersed to India or had fled to villages. Troops had shelled and destroyed public buildings and bazaars at random, and commercial life was at a virtual standstill.

Paralysis of the East Pakistan economy. Although the central government has ordered the opening of mills, the mills typically work only half a shift daily. Jute and tea production, principal earners of foreign exchange, is at a fraction of its normal level.

Active guerrilla resistance by those favoring an independent East Pakistan. Collaborators with the martial law regime are in mortal danger, and two British tea planters have been murdered for attempting to continue normal operations. A bomb was thrown in the courtyard of the Intercontinental Hotel in Dacca while the Bank-Fund team was there, but no one was hurt.

A demolished transportation network. About 60 percent of East Pakistan goods normally move by rail, but the train system is barely functioning. At least 13 key bridges have been blown up by guerrillas, and the regime has made only kutcha or makeshift repairs.

A strong likelihood of widespread famine this fall. It will occur not because of a lack of rice, the staple diet of Bengali East Pakistan, but because the transportation network is so deeply damaged and distribution systems have broken down.

Ignorance by the Yahya regime as to the true conditions in East Pakistan and the state of world opinion. Pakistan's envoys abroad, with few exceptions, are said to be minimizing the widespread revulsion over the violence in their country.

Cargill himself is understood to have had a heated meeting with Yahya on June 14. Cargill is said to have disputed a Yahya forecast that life will return to normal by September.

The World Bank official reportedly said that Pakistan could not use aid effectively at this point. Yahya, who had indicated he wanted $100 million now and more to follow, is known to have exploded at this statement and hotly asserted that the conclusion amounted to interference in Pakistan's internal affairs.

Among other things, the Bank-Fund mission is known to be disturbed by Pakistan's rising military budget. Arms outlays last year were 3 billion rupees, or $630 million at the official exchange rate, and are planned at 3.4 billion rupees, or 6710 million, this year.

The mission suspects that Pakistan is spending what is left of its foreign exchange to buy arms abroad, notably fighter planes and sophisticated antisubmarine weapons systems from France.