NEW DELHI.-India has mounted a broad diplomatic and publicity campaign to try to mobilize world pressure on Pakistan to halt the refugee flow from the East Pakistan.

More than three million Bengalis have poured into India, and the Indians charge that the refugees have fled as a result of the two-month-old drive against the Bengali independence movement in the east.

The message that is being spread with unusual vigor in the local press here and by Indian diplomats abroad is that unless the world community persuades Pakistan to stop her "deliberate campaign of terror" and "deliberate expulsion" of Bengalis, India will be "forced to act to protect our national interests."

Indian officials do not elaborate on what "forced to act" means, and foreign diplomats here doubt that New Delhi has made any definite plans for its next step if world response proves disappointing.

But the refugee and border situation is becoming more serious, and while it is clear that neither India nor Pakistan wants another war, observers here do not rule out the possibility. Should a military clash erupt, India is hoping that both Indian public opinion and world opinion will have been prepared for it and will understand India's case.

PRESSURE ON GOVERNMENT

Another apparent reason for the tough stance is to satisfy the wide public sympathy in India for the Bengali independence struggle and to relieve some of the resultant pressure on the Government to grant recognition to the recently proclaimed government of Bangla Desh, or Bengal nation, the Bengali name the insurgents have given to East Pakistan.

Prime Minister Indira Gandhi has said she feels recognition at this time would be a mistake because it would lend credence to Pakistan's charge that the independence movement was engineered by India in order to dismember Pakistan. The pressure for recognition will be renewed by opposition parties when the next session of Parliament opens on Monday, and Mrs. Gandhi will now enter the session with fresh ammunition.

The Indian diplomatic offensive, which began this week, was preceded by a protest note to Pakistan, which said that the military action in East Pakistan "has created a human problem of unparalleled magnitude which is capable of producing serious repercussions in the area leading to a threat to peace in the region." In a speech last Tuesday, Mrs. Gandhi said, "If a situation was forced upon us, then we are fully prepared to fight."

REFUGEES 60 PERCENT HINDU

The Indian Government believes-and its ambassadors reportedly have been instructed to convey to foreign Governments that the Pakistani Army is now calculatedly terrorizing certain unwanted elements in the East Pakistan population, such as the minority Hindus, so that they will flee across the border and place grave strains on India's economic and social fabric.

The refugees are about 60 percent Hindu and 40 percent Moslem. From their composition and their accounts of what happened in their villages, it would appear that the army's main targets are students, young people, intellectuals, party workers for the now-banned Awami League and Hindus, who voted strongly for the pro- autonomy Awami League in last December's election and who have always been regarded as pro-India by the West Pakistanis.

Some West Pakistani newspapers have been attempting recently to blame the Hindu vote for setting off the conflict. The papers argue that Hindus should never have been given an equal franchise in an Islamic state. In a statement on the refugees yesterday, Pakistanis President, Agha Mohammed Yahya Khan, said that "bona fide Pakistani citizens are welcome to return to their homes."'

President Yahya repeated Pakistan's contention that many of the refugees are Indian infiltrators who entered East Pakistan to help the insurgents. He said violence by anti-state elements had forced a number of innocent persons to seek shelter in India, and he contended that other Bengalis "were encouraged by India to leave with the object of disrupting East Pakistan's economic life."

COST CONCERNS INDIA

Home of the refugees this correspondent interviewed on a recent three-day tour of refugee camps mentioned any factor but the Pakistan Army in explaining why they fled East Pakistan.

The cost of sheltering and feeding the Bengali refugees- estimated at hundreds of millions of dollars a year-is considered prohibitive for India, whose resources are already strained by a population of 550 million India is even more worried about the social tensions and security problems.