NEW DELHI.-Indian military experts are offering three alternative solutions to the trigger-tense situation on the East Pakistan border.

1 To recognize the Bangla Desh provisional government in East Pakistan and send in trained refugee guerrillas.

2. To order the Indian Army to wage a "limited war" to clear a 50-mile deep strip in East Bengal for the 3,500,000 refugees who have streamed into India.

3. To give all-out military support to Bangla Desh and help the provisional government to clear the Pakistan Army from the whole of East Bengal.

All three plans have major flaws.

The first is handicapped by the refugees being unready for warfare for another three months. Prime Minister Indira Gandhi has also ruled out recognition of Bangla Desh for the present in spite of opposition pressure.

NEHRU REJECTED PROPOSAL

The second option is similar to a proposal rejected in 1951 by Mrs. Gandhi s father, the late Jawaharlal Nehru. There also is doubt about the willingness of refugees to return to an area of continuous fighting.

The countervailing view to the third plan is that while military experts think that India can easily fight a war on two fronts with East and West Pakistan, it cannot fight on a third front if Communist China came to the aid of its Pakistan ally.

India has launched a diplomatic offensive to persuade Pakistan to create political conditions for the refugees to return, and the United States also is urging Pakistan to make a political settlement.

Meanwhile the border situation is worsening. The Indian Army has replaced the paramilitary border units in some sections, and antiaircraft guns have been placed in key areas of West Bengal.

[Meanwhile, Reuter indicates tension is high along India's frontier with East Pakistan after the Press Trust of Indian reported that Indian security forces killed 120 Pakistani troops who crossed the border on May 26.

[The news agency reporting from the northeastern Indian town of Shillong said the clashes occurred in the early part of the week. ]