AGARTALA, India— For more than a decade, India has secretly provided arms and money to tribal insurgents fighting for an autonomous state in Bangladesh, rebels given sanctuary in this border area say.

A senior security official here confirmed the assistance and said an undetermined number of rebel fighters had stayed along the border near camps of Indian paramilitary forces.

''The Government is giving them help,'' the official added, without elaborating.

The rebels, who are mostly Buddhists, belong to the Chakma and other tribes in the Chittagong Hills of Bangladesh. They say they are being persecuted and pushed off their fertile land by an influx of ethnic Bengali Bangladeshis, who are overwhelmingly Muslim. Elections Are Planned

President H. M. Ershad of Bangladesh is planning to hold elections on June 25 to give some local autonomy to the Chittagong Hill Tracts, but the Shanti Bahini, the guerrilla organization fighting the Government, has called for a boycott of the vote and declared it will disrupt balloting.

A spokesman for the rebels said Indian officials began to provide arms and money in 1976, after the assassination in a military coup of Sheik Mujibur Rahman, Bangladesh's first President and a friend of India.

The spokesman, Bimal Chakma, said the Indian Government had not given as many weapons as were needed. ''At the beginning we got some consideration, but it is very low compared with what we need.''

The Shanti Bahini has an estimated 500 guerrillas. Over the years, the insurgents have increased their armory by capturing weapons through raids on Bangladesh military units. The rebels in the Chittagong Hill Tracts also picked up large caches of Chinese semi-automatic weapons during the 1971 Indo-Pakistan war. Past Help for Pakistani Rebels

India also armed, trained and financed ethnic Bengali rebels seeking to break away from Pakistan, of which Bangladesh, then East Pakistan, was a part. The guerrilla attacks escalated into a war between India and Pakistan in 1971 after 10 million people fled military atrocities into India. Pakistani troops were routed and Bangladesh was created.

The Shanti Bahini, which means peace corps in the Bengali language, was formed in 1972 after a rejection of demands for autonomy, preferential treatment and an end to the Muslim influx. The Shanti Bahini says it has killed more than 500 members of the Bangladeshi military and the police as well as Muslim settlers.

''We are not separatists and we do not want armed intervention by India,'' said Mr. Chakma, the rebel spokesman. He said they wanted a stop to Muslim settlers, protection of the region's demographic character, free elections and extensive economic and political powers.

Sudhir Ranjan Majumdar, the Chief Minister or top elected official of Tripura state in northeast India, said the state did not ''harbor any Shanti Bahini, although their political wing is here.''

''We have a foreign mission here to consult with the Indian Government,'' a rebel official said. ''When there are bad combing operations by the Bangladesh army our fighters cross the border for security. They also come on leave from the campaigns.'' An Exodus to India

Since 1986, India has absorbed more than 51,000 refugee tribespeople, nearly 9,000 of them in the last two weeks, as they flee what is said to be military repression in the region. The refugees include supporters of the Shanti Bahini and leaders of the movement's political wing, the Jana Sanghata Samiti or People's Struggle Organization.

Bangladesh is the world's most densely populated region and one of its poorest. Since it was formed, Muslim settlers have been moving from other parts of the country to the lightly populated Chittagong Hill Tracts. The influx has changed the ethnic composition of the place and brought tension and clashes in its wake.

The current population of the Chittagong Hill Tracts is about one million, with nearly 600,000 tribespeople. The rest are Muslim settlers.

Bangladesh has stepped up a bitter army campaign against the Chakmas, sending them fleeing into India several times in the last 17 years. The 1986 exodus was the biggest. Rights Violations Reported

Amnesty International, the human rights organization, has reported serious violations of human rights in the Chittagong Hill Tracts by Bangladeshi military personnel, including rape, torture and indiscriminate shooting. Recent refugees say the assaults on women, capture of farmland by Muslim settlers and killing of Chakmas is continuing.

The weariness with fighting is showing and the Shanti Bahini held six rounds of talks over the last year with Bangladeshi officials. However, there has been little progress, Mr. Chakma said.

Map of India and Bangladesh indicating the Chittagong Hills. (NYT)