Delhi, Nov. 23. In what appears to be the beginning of an undeclared war Indian troops disguised as Bengali guerrillas have moved into East Pakistan at brigade strength and have occupied a slice of territory north-west of the Pakistan garrison town of Jessore, informed sources said today. As a result of the intrusion Pakistan today declared a national emergency. The Indian Government expects Pakistan to make a counter strike in Kashmir and on the western front at any moment, an action which would put the stamp of formality on an all-out and bitter war on all fronts.

Radio Pakistan and an official spokesman in Dacca said today that fierce battles are raging in Jessore, Chittagong, Rangpur and Sylhet areas and that Indian troops had marched across the border supported by tanks. In spite of allegations and counter allegations it is now obvious that Indian and Pakistan armour units have been locked in a serious and fierce tank battle north-west of Jessore during the past few days. Informed sources suggest that Indian Gnat aircraft intercepted Pakistan Sabre jets yesterday when Pakistan armour units called for air support against advancing Indian tanks.

Mr. Vidya Charan Shukkla, India’s Minister of State for Defence confirmed in Parliament today that three Pakistan Sabres had been shot down in the Boyra district yesterday afternoon by Gnat fighters. However, he denied that Indian troops had moved across the border and went on to claim that the Sabres had been shot down about three miles inside Indian territory. He also denied that an undeclared war had broken out. To authenticate Indian successes in the air the Government today released the names of two Pakistani pilots who baled out over Indian territory during the air battle.

There are now obvious signs in Delhi that after exercising restraints for eight months Mrs. Gandhi, the Indian Prime Minister, is convinced the efforts of the international community to achieve a political solution to the East Bengal crisis have failed and she has no other recourse but to embark upon a military action. It would appear that the Indian Government has several objectives in mind. India certainly does not want to make a formal declaration of war and it would seem as though troops disguised as guerrillas have been sent across the border with the express purpose of provoking the Pakistanis into acts which would lead to war.

Pakistanis, if provoked in East Pakistan to the point of desperation, would have to hit back on the more favourable fighting ground of the western front. This would precipitate a formal war which would automatically bring international pressure to bear on both sides. According to Indian strategy, the moment Pakistanis strike in the west the Government will recognize the provisional government of Bangladesh, sign an already prepared defence pact with the Bengalis, and then on the invitation of the elected representatives of the East Pakistanis, India would feel justified in formally marching into the turbulent province.

Both the Pakistan and Indian armies are poised at full strength along the western front adjoining the Indian states of Punjab, Gujrat, Rajasthan and along the cease-fire line in the disputed territory of Kashmir. Delhi’s international airport has been surrounded by anti-aircraft units and soviet sam-2 and sam-3 units. It is estimated that the Indians have 14 divisions deployed on the western front, and nine divisions on the eastern front. Another seven divisions of mountain troops are still deployed on the Chinese border. Pakistan has an estimated four divisions in the eastern province and another 12 divisions are deployed along the border on the western front.

Indian news agencies, briefed by spokesman for the defence forces, reported tonight that the “East Bengal guerrillas” had launched a large-scale offensive on the Nadia (Kushtia) district in the vicinity of the border area adjoining the Indian town of Krishnagar. According to the Press Trust of India, the guerrillas - who admitted to me last month that they were capable of launching a conventional military offensive against President Yahya Khan’s well trained army for at least two years - have now almost captured the strong garrison-town of Jessore.