NEW DELHI. NOV. 30—A large combined force of Indian infantry and tanks was fighting’ in East Pakistan for the fourth day today. In size and duration the engagement is the gravest so far in the fighting between India and Pakistan.

An Indian military communiqué asserted that the Indian force, which penetrated into the northwestern part of East Pakistan near the border town of Hilli on Saturday, had repulsed a Pakistani counter attack aimed at dislodging the Indians.

“Our troops are still in their territory,” said an Indian spokesman, who reported that fighting today had dwindled to artillery exchanges. The communiqué described today's action as “sporadic fighting.”

India has not disclosed the size of the force that crossed the East Pakistani border Saturday, but informed sources believe it is a reinforced infantry brigade, accompanied by a regiment of medium tanks. There arc 2,900 men in brigade and 45 tanks in an Indian armored regiment.

India has described the incursion near Hilli—about 185 miles north of Calcutta—as justified defensive action.

Information Is Scarce

Reliable military information from East Pakistan is very scarce and the situation there veiled by a cloud of rhetoric, conflicting claims and unanswered questions.

However, independent information believed to be reliable indicated that the fighting near Hilli was on a larger scale than official statements have implied. If a reinforced Indian brigade is involved, more than 3,000 riflemen must be involved on the Indian side. Official Indian statements assert that the Pakistanis are using a brigade in the area.

The Indians have said that since Saturday they have destroyed five Pakistani tanks of a squadron of 14. Today an Indian spokesman said that the remnants of the Pakistani tank squadron had been withdrawn because of the “mauling” it had received. India says that only one of her tanks was damaged, by an antitank mine.

Basis For the Claims

The unofficial report that full regiment of Russian‐made T‐55 medium tanks was being used by India helps to explain the basis of the Indian claims.

The Pakistanis are using the Chaffee, or M‐24 tank in the area. This is a light tank with relatively thin armor. It is an obsolescent American vehicle that was withdrawn from the United States inventory in 1947.

The T‐55 outclasses the Chaffee in both Its gun and its plating. Most of Pakistan's best tanks are in West Pakistan.

Pakistan is believed to have about four divisions, or a total of 70,000 to 80,000 regular troops, in East Pakistan. India is believed to have deployed seven divisions and several independent units around East Pakistan.

Pakistani Disadvantage

Pakistan is at such a military disadvantage in the East that there has been increasing speculation that she might attack India on India's western frontier, where both nations have larger forces.

The purpose of a Pakistani thrust in the West might be to try to seize a piece of the coveted Kashmir Valley—over which the two countries have fought twice—in retribution for the loss of East Pakistan. Many analysts believe that a fight in the West could end in a bloody stalemate.

India last week announced that she was adopting a policy of “defensive” border crossings in the East in response to what she says are Pakistani military thrusts and threats.

One result of such crossings, of which there have been several, would to be to tie up Pakistani units near the border and limit their effectiveness in fighting the Bengali guerrillas.

Some experts say they discern other motives in recent Indian actions, one of which is to threaten important lines of communication. If these lines were cut the Pakistani divisions would be difficult to supply, reinforce or deploy.

For instance, in the Hilli area, the Indian attack seems to threaten the north‐south rail line, which runs slightly east of the town. If either Indian or Bengali insurgent forces got astride this railway, Pakistani forces in the Hilli area and to the north would be cut off from Jessore to the south.

In the southeastern part of East Pakistan insurgent forces are known to have captured a thumb of East Pakistani territory that juts into India near the town of Fenny.

These forces are now only a few miles from Fenny, which lies on the vital rail line from the main port of Chittagong to the provincial capital of Dacca. Should this railroad be cut, the Pakistani supply situation could become uncomfortable.