NEW DELHI, Dec. 7—In her first major offensive of the four‐day‐old war, Pakistan began a large‐scale tank and infantry attack today against Indian troops guarding a key road in southwestern Kashmir, India reported.

An Indian military spokesman said that Indian troops had fallen back five miles to prepared positions after inflicting what he described as “heavy casualties” on the Pakistanis around the town of Chhamb, near Jammu.

[In Rawalpindi, President Agha Mohammad Yahya Khan appointed Nurul Amin, a Bengali civilian, as Prime Minister and Zulfikar Ali Bhutto, a former Foreign Minister, as Deputy Prime Minister. But the President will retain real power in Pakistan.]

The armored thrust at Chhamb was similar to the one with which Pakistan began the 22‐day war in September, 1965. Chhamb screens India's only road link with western Kashmir, a road that runs through Aknoor to Poonch. If the Pakistani force can keep moving and reach Aknoor, about 12 miles to the east, or the road northwest of that town, large numbers of Indian troops in western Kashmir would be isolated.

The Pakistani attack came as India announced the fall of several important cities in East Pakistan, including a major Pakistani headquarters at Jessore. The capture of Jessore virtually insured Indian control of about half of East Pakistan.

The Indians also announced two victories on the western front, where there had been only small skirmishes and probing actions by the two sides until today.

In the Kargil area on the cease‐fire line in northern Kashmir, the Indians claimed to have captured several Pakistani mountain outposts. And in southern Rajasthan, an Indian armored column was reported to have advanced 34 miles across the desert toward Hyderabad, capturing two small Pakistani towns.

Attack on Plane Denied

There were also these other developments:

¶The Indian Defense Minister, Jagjivan Ram, denied that Indian aircraft had fired on a Canadian C‐130 airplane that had flown from Bangkok to Dacca to try to evacuate families of United Nations personnel trapped in the city. The Canadian plane was reportedly fired upon by unknown aircraft as it was flying over Dacca.

¶The Indian Navy reported having detained six more merchant vessels in the Bay of Bengal that were said to be under charter to the Pakistani Gulf Shipping Corporation. An Indian spokesman said he did not know the nationality of the owners of the vessels. Yesterday the Indians detained an American ship, the Expeditor, on suspicion that it was carrying cargo destined for the East Pakistani port of Chittagong.

¶The kingdom of Bhutan followed India's lead and became the second country to recognize the government set up by East Pakistani rebel leaders, known as Bangla Desh (Bengali Nation), as the official government of East Pakistan. Under a 1949 treaty, Bhutan is bound to accept India's advice in foreign affairs, though an official Indian spokesman denied that India had given any advice in this case.

¶Thirty members of the Indian Parliament from different political parties demonstrated for 15 minutes outside the United States Embassy, criticizing the United States for its action in the United Nations Security Council in trying to arrange a cease‐fire. The legislators charged that Washington was unfairly trying to brand India as the aggressor.

The demonstration at the embassy was the latest outbreak of anti‐American feeling, which has been running high here. Indians are resentful that Washington has not openly sympathized with India's support for the East Pakistanis struggle for independence, which began last spring.

In the Chhamb attack, the Pakistanis reportedly thrust division of infantry, three armored regiments totaling about 150 tanks, and large quantities of artillery across the border and quickly captured the town of Mandiala.

The Indians then retreated across the shallow Munnawar Tawi River and abandoned the town of Chhamb. In heavy fighting, which was said to be continuing at nightfall, the Indians reported they had knocked out 33 Pakistani T‐59 tanks and had lost 15 tanks of their own.

Orderly Pullback Reported

According to an official spokesman, the Indian withdrawal was orderly and stopped at heavily fortified positions on the other side of the river.

The Chhamb area is strategically important because the terrain in the area gives access to an armored force trying to push eastward towards Aknoor and the road to Poonch. It is also the route to the even more strategically important town of Jammu, which lies astride the only highway from north India to the Vale of Kashmir and Ladakh.

Despite the size of today's attack, experts in New Delhi felt that it was still not the major offensive that the Indians have expected Pakistan to open in retaliation for Indian victories in East Pakistan. Such an attack, these experts believe, will probably come, farther south in the Punjab, closer to major Indian population centers.

The Indians reported that there had been no Pakistani air raids in the west during daylight hours today, though Pakistani jets staged 15 raids on Indian air bases last night under cover of darkness. One more enemy plane was shot down today, the Indian command announced, bringing total Pakistani aircraft losses to 53, it said.

The Indian Air Force said it had carried out raids on enemy air bases at Karachi, Rawalpindi and other cities, as well as attacking an enemy supply train and destroying 15 railroad cars. Three Indian jets were reported lost over West Pakistan, bringing total Indian losses to 22, according to the official count.