NEW DELHI, May 22 — The problem of caste prejudice here is as ancient as the Hindu texts. The efforts to redress it date from the formation of modern India nearly 59 years ago. Today — as India enjoys awesome rates of economic progress and confronts the challenge of spreading the benefits to its needy majority — the nation faces a polarizing totem of public policy: a government plan to extend college admission quotas to certain “backward” castes.

Affirmative action is in some ways an even more emotional issue in India than in the United States. In recent weeks, a proposal to extend quotas for admission to some of the country’s flagship, federally financed universities has caused fresh turmoil.

Protests — particularly by medical students who say merit should be the only basis for admission to India’s intensely competitive medical schools — have spread across the country and, here in the capital, hobbled public health services. Advocates and opponents of the measure have exchanged often ugly rants.

For the government, redressing age-old caste discrimination has become mired in divisive politics. The government has said it will not back down from its proposal.

Caste-based quotas are not new. As authorized by its Constitution, India has long set aside 22.5 percent of public university seats, including those at the most elite institutions, for the lowest castes on the Hindu social ladder and indigenous tribes. Quotas also apply to government jobs and elective office.

The latest proposal extends that principle by setting aside an additional 27 percent of seats for a group known in the bizarre parlance of Indian bureaucracy as “other backward classes,” or O.B.C.’s.

The new quotas would apply to the country’s most competitive federally financed universities, including the Indian Institutes of Technology, the Indian Institutes of Management and some elite medical colleges.

Medical students have been particularly outraged because the plan would further restrict the limited number of seats. Medical education in India begins with a five-year undergraduate program, and the proposal could affect students’ chances of completing their training.

The central lawn of the All India Institute of Medical Sciences, the pre-eminent public hospital, was occupied Friday by medical students on the fifth day of a strike that began last week and continued on Monday. “My merit is my caste. What is yours?” read one T-shirt.

The quota advocates have also mobilized. On Friday in Patna, a group of them clashed with the police. Earlier in the week they faced off against antiquota medical students at the All India Institute of Medical Sciences, arguing that it was against the law for doctors to strike.

Prime Minister Manmohan Singh has shied away from commenting explicitly on the proposal, but has instead appointed a three-member advisory committee to study the measure and its repercussions.

Asked for a comment, his office cited only a speech to a Harvard alumni group on March 25, in which Mr. Singh suggested that he favored an expansion of scholarships for deserving students based on merit and means.

“Government can and must balance the elitism of meritocracy by facilitating those at the bottom of the social pyramid to rise to the apex of an academic pyramid,” he said in that speech.

The debate over college admission quotas is particularly salient. Most Indians are young, and how social policy addresses their aspirations is among the most pressing challenges for the government.

As a compromise, lawmakers have suggested that the flagship universities could expand the total number of seats. That, of course, would raise a new set of challenges, including hiring more professors.

It has not gone unnoticed that at a time when the Indian economy is on the fast track to liberalization, the higher education system continues to be highly regulated.

In recent months there have also been suggestions — but no explicit measures — to introduce quotas in the private sector as well, prompting anxious opposition from business leaders.

Affirmative action in India is different in important ways from affirmative action in the United States. In the intricate pecking order of Indian society, those who belong to the cow herder caste, which falls under the “other backward” category, are in fact several levels above the tailor caste.

Tailors, in turn, enjoy a higher status than waste collectors, who, despite a ban, continue to carry human waste on their heads in parts of the country. They are considered untouchable according to Hindu custom.

While caste no longer necessarily determines a person’s vocation, it does determine to a large extent whom one marries, dines with and, most important for this debate, votes for. The “other backward castes” are a powerful voting bloc in many parts of India, making the outcome of the current debate of particular importance to Indian politicians.

Finally, unlike affirmative action in America, India’s in effect begins and ends with quotas. Whether quotas are in fact the best and most effective means to promote access to marginalized young Indians is still a matter of debate.

Supporters of the latest measure say that in an unequal society, only explicit set-asides can open doors. Where there are no mandatory quotas, in the private sector for instance, or in the news media, they argue, upper castes continue to dominate.

“Caste is qualification for few; caste is disqualification for many,” said Bhalchandra Mungekar, an economist on the national government’s Planning Commission. “A small microscopic elite of Indian society is determined to perpetuate its monopoly over the privileges.”

The opponents say set-asides would diminish the quality of India’s best universities and divide students along caste lines.

“Why after 55 years are we still thinking in terms of caste-based reservation?” demanded Poojan Aggarwal, a third-year student at Safdarjung Medical College here. “We should talk now of total meritocracy. We know on this issue none of the political parties will support us.”

Some people worry that quotas — or reservations, as they are sometimes called — may not be the ideal way to expand access to the best universities. Caste is not the only inhibition, after all; income, poor public services and other factors also deny millions of Indians access to sound basic education.

“We recognize proactive measures, some form of affirmative action, needs to be taken to make them socially inclusive,” said Pratap Bhanu Mehta, a member of the Knowledge Commission who resigned on Monday because of differences with the prime minister’s office over these quotas. “We also recognize that the only instrument for affirmative action we’ve used so far, which is reservations, has actually not produced the kind of positive results we would have hoped.”

Most members of the commission, which advises the prime minister on higher education and other issues, oppose the proposed measure. The commission has suggested that the government explore other means to expand access, like improving primary and secondary education, before resorting to more quotas.

“This is short-circuiting the debate about what needs to be done to have a much more effective affirmative action policy,” Mr. Mehta said. “Frankly, the other underlying thing for us is that reservations have become a way of displacing responsibility. We are not talking about all the other things that need to be done to improve access.”

Hari Kumar contributed reporting for this article.