NEW DELHI, AUG. 24 -- Police used tear gas and batons to disperse an estimated 2,000 students who hijacked city buses and tried to storm India's parliament today in a swelling protest against a government affirmative action program.

Streets near the Indian capital's universities were littered this evening with glass and smashed buses used by the students as barricades. Despite snarled traffic and dozens of reported arrests and injuries, order appeared to have been restored by nightfall.

The violent protests reflected the intense reaction of many students around India to Prime Minister V.P. Singh's recent announcement that he intends to set aside almost half of all government jobs for applicants from lower castes and aboriginal tribes.

Student protesters from upper and middle castes say the plan will lock them out of cherished jobs in the country's vast public bureaucracy, which traditionally has been dominated by India's socially privileged classes.

The students also argue that by focusing on caste rather than economic need, Singh's plan unfairly discriminates against destitute job seekers while exacerbating caste tensions in India's deeply stratified society.

Singh and his cabinet have defended their program by arguing that job quotas are the only way to effectively redress discrimination against lower castes, particularly India's more than 100 million shunned "untouchable" caste members. They say the government jobs to be set aside represent a fraction of the country's employment opportunities.

While reopening a divisive and painful debate about the power of caste to control lives and opportunities in India, the affirmative action program and the student protests have added a new element of instability to the country's shaky political alignments.

Hindu conservatives who provide tentative support to Singh's minority government have opposed aspects of the affirmative action plan and appear set to capitalize on the anger it has generated among socially privileged but economically backward Hindus in northern India.

Protests against the plan have been strong in the heavily populated regions of northern India, where the Hindu conservatives must win new adherents if they are to make a serious challenge for power in New Delhi.