CALCUTTA.- Senior Indian army officers are taking it for granted that a successful guerrilla campaign can be mounted in East Pakistan and the India will aid the insurgents,

Such aid will not be announced or even acknowledged by India's government, well informed sources here believe. However, army officers apparently have decided that the opportunity provided by the East Pakistan fighting cannot be passed up.

In several conversations, officers have assumed that fighting will go on at a low level and that India will take steps to ensure that the guerrilla leadership is non-Communist.

The threat of a Communist top command taking over the East Bengali resistance movement is being used here as a justification for giving arms and training to non- Communist fighters.

One officer conceded that it would be a difficult intelligence task to identify effective non-Communist leaders or potential leaders from among the hundreds of thousands who have landed in India after fleeing Pakistan army's attacks.

TO BE EXPECTED

"Some mistakes will be made," he said. "And there will be heavy casualties among the first groups, but that is to be expected in this sort of game. Eventually the right types can emerge.

He predicted that up to three-quarters or the first low-level cadre chosen to infiltrate East Pakistan and harass the Pakistan army will be killed or found unsuitable.

The expectation here is that the guerrilla fighting will last a long time, but that the East Bengalis will eventually force the Pakistan army to give up. "I am talking about several years, maybe five, but at some time they (Pakistan's army) will lose," one officer remarked.

The Indian army does not appear to be giving any assistance to the Bengalis at present, other than sheltering them in army camps close to the border where they are safe from Pakistan army pursuit.

While the Indian and Pakistani governments and newspapers exchange charges over alleged incidents of Pakistan army shooting across the border into India and Indian interference in Pakistan's affairs, the Indian army is apparently being very careful to avoid any possible direct clash.

NORMAL STRENGTH

Along the West Bengal-East Pakistan border, for example, there appear to be no more than the normal number of Indian border security troops. Regular army units have not been shifted close to the frontier although about 40,000 men are available in West Bengal.

Instead of taking military measures to beef up its border forces, the Indian army apparently has been concentrating on gathering intelligence about the East Pakistan fighting and the leaders or both sides. As the army sees It, Pakistan will never be able to reassert civil authority over the Eastern wing. Therefore, the reasoning goes, after some time the East will become free as either a pro-India nation or an ally or Peking.

China will cease its current support of West Pakistan, it is believed here, If Peking gains control of the East Pakistan resistance and turns it to Chinese political ends.

WESTERNERS AGREE

In addition to the army, several Indian politicians and Western analysts believe in this scenario and think that India cannot afford pro-Peking revolutionary state in East Pakistan.

An immediate military consequence would be the increased threat to India's northeast frontier and the Assam, Indians believe. The narrow corridor of West Bengal connecting Assam to the bulk of India would be very vulnerable if China had military access to East Pakistan. Without that corridor, supplying the Indian divisions facing China along the northeast frontier would be almost impossible.

There would also be a less direct threat to the corridor, officials here believe, in the form of greater agitation for an independent West Bengal or a union of West Bengal and East Pakistan in a larger Bengali nation.

Maoist Naxalite terrorists are already strong enough in West Bengal to concern the army. And they would gain a friendly neighbor should Communists take hold across the border. The Naxalites are widely rumored to have sent cadres into East Pakistan to train resistance fighters, but there has been no conclusive evidence of such activity.

The Indian army, and most Indian politicians, discount the - possibility that East Pakistan guerrillas will never become effective. They argue that the estimated 400,000 refugees already in India provides a manpower pool that inevitably will produce able resistance fighters. The brutality of the Pakistan army has made it Impossible for large numbers of these people to live under army domination, officials here believe.

The reported Pakistan army atrocities puzzle India's officers. Although the two nations are enemies, many of the senior officers know their counterparts and they find it difficult to believe that such widespread massacres have been condoned.

Several officers suggest that Pakistan army discipline must have broken down and that small units have been killing without the authorization of their senior officers. However, all the evidence to emerge from East Pakistan points to a top-level Pakistan decision to use mass killings in an attempt to cow the remaining civilians.