WASHINGTON, Nov. 23—United States officials said today that information available to the highest levels of the Government indicated that Indian regular forces had crossed into East Pakistan and were either spearheading or closely collaborating with Bengali guerrillas in fighting the Pakistani Army there.

At the same time they disputed Pakistani charges that India had launched a full‐scale “invasion” of East Pakistan. Full‐scale war between India and Pakistan is possible, even probable, they said—but it has not yet reached that point.

Nawabzada A. M. Raza, the Pakistani Ambassador to the United States, contended in a news conference at his Embassy here today that, starting Sunday. troops from the Indian 9th, 23d and 57th division—supported by armor and air cover‐had attacked East Pakistan on “three fronts.” He listed Jessore, Rangpur, Sylhet and the Chittagong hill tracts as areas being attacked.

The Ambassador, who is 66 tears old and who retired from the Pakistani Army as a major general in 1947, called on the United States to decide what it could do to help Pakistan. He cited “bilateral agreements” between Pakistan and the United States, but when pressed for details conceded, “I'm not too much in the picture.”

Charles W. Bray 3d, the State Department spokesman, said that the United States was “concerned” by indications of “Considerable military activity taking place along the Indian-Pakistani frontier.”

In Touch With Soviet

While conceding that the United States had “little” independent information from the area, Mr. Bray said that the United States was in touch with both India and Pakistan as well as with the Soviet Union and others of the Big Four Powers, a reference to Britain and France.

Mr. Bray said it was too soon to say whether the United States might seek a Security Council meeting on the clashes. He also ruled out United States talks with mainland China on the issue. When asked why, he said:

“We thought it was more important to be in touch with other powers.”

There were indications that the United States might be seeking to negotiate for the placing of United Nations observers on both sides of the Indian‐East Pakistani border, although Mr. Bray declined specific comment. India has consistently refused to accept United Nations observers on her soil, but Pakistan has permitted a force of five observers to operate in East Pakistan and to inspect the border areas.

The force is under the command of John Kelly, an Irish national and a former commando officer. It reports directly to U Thant, Secretary General of the United Nations.

News Called Fragmentary

United States sources reported that fighting appeared to have intensified sharply within the last 48 hours between the Indian border and the East Pakistan city of Jessore, approximately 20 miles east of the border. They said that information reaching here is still fragmentary.

The proportion of Indian regulars and Bengali guerrillas in the fighting is not known, but there seems little doubt that Indian regular troops are now involved. The guerrillas, who call themselves Mukhti Bahini (Liberation Forces), are the fighting arm of Bangla Desh, the Bengali separatist movement that seeks independence from Pakistan.

‘Analysts here said that the attacking forces are reported to have halted approximately 16 miles inside East Pakistan, or half way to Jessore. They are not believed at present to be trying to drive north on to Jessore itself.

Reports here also indicate scattered clashes at other points along the 1,400‐mile border between India and East Pakistan.

Last March 25 President Agha Mohammad Yahya Khan sent Pakistani troops into East Pakistan to quell an autonomy movement led by Sheik Mujibur Rahman, head of the Awami League. Since then the Awami League, which is widely backed by the preponderantly Bengali people of East Pakistan, has been banned. Sheik Mujib and several associates have been imprisoned and the protracted civil strife has caused millions of East Pakistanis to flee into neighboring India.

The Pakistani Government has said that slightly more than two million refugees have crossed into India. However, the Indian Government asserts that the number exceeds nine million. Pointing to the heavy burden on her own economy, India has demanded that President Yahya solve the problem by direct talks with Sheik Mujib and his associates—a demand that President Yahya has so far rejected. Both countries have mobilized as tension continued to mount.

“Our estimate is that India is deliberately stepping up the pressure on Yahya Khan to force him to reach a political settlement with Sheik Mujib,” one qualified informant said. “They're out to wreck his timetable.”