The dusty backyards of the Gajara colony of low-caste Harijans were strewn with rocks and lethal-looking bottles of acid, remnants of a barrage of missiles hurled at the ramshackle slums the night before in the latest caste war of this crowded mill city in western India.

Small knots of Harijan laborers and outcaste Chandalas, or Untouchables, gathered under shade trees and glared angrily at their neighbors barely 100 feet across a barbed-wire fence hastily erected by police to keep the two groups apart. They spoke bitterly about the eight men and women they said had been injured in the attack, and vowed to fight back if provoked again.

Across the wire fence and beyond a dirt alley patrolled by nervous policemen, groups of higher caste Patels of the Vaishya, or shopkeeping, caste glared back at the Harijans. Standing amid a carpet of broken bricks and shattered windows of their tidy bungalows, they also spoke bitterly of the four-hour rock fight that they said the Harijans had initiated.

But the Patels had another complaint: one of reverse discrimination they said has resulted from a government quota system designed to place more low-caste, economically deprived and socially "backward" Indians in university classes and civil service jobs.

"They get 35 percent on their examinations and get into government service. We get 85 percent and do not get into the service," complained one angry Patel in a rhetorical outburst reminiscent of the controversial Allan P. Bakke reverse discrimination case at the University of California's Davis Medical School a decade ago. In that case, the Supreme Court ruled that the medical school's policy of reserving 16 of 100 places in the entering class for minorities was discriminatory.

Ahmedabad, the city where Mohandas K. (Mahatma) Gandhi made famous his principles of nonviolence and equality and vowed to erase castes from Hindu culture, has been turned into a battleground during the past month over the government's attempts to raise college and public employment quotas for lower caste Indians, members of indigenous tribes and so-called backward classes of the poor.

At least 30 persons have been killed in riots since March 19 and scores of shops have been burned by mobs. In the violence, religious hatred frequently has been commingled with the issue of the controversial quota system.

Most of this city of 2.8 million, the commercial hub of Gujarat State, is paralyzed under a round-the-clock curfew enforced by Indian Army troops in full battle gear, who took over from the beleaguered local police Wednesday.

The normally teeming Walled City in the heart of Ahmedabad is virtually deserted day and night, its streets cluttered with smoldering barricades. Angry young men, clutching bricks and gasoline-filled bottles, lurk in the shadows of alleys waiting for Army and police patrols to drive into range.

In the old city's main thoroughfare, paradoxically called Gandhi Road, youths taunted a squad of policemen sitting in a truck behind a heavy mesh screen, and scattered into the narrow side streets only when a convoy of Army vehicles came into sight.

"Nobody has bothered about Mahatma Gandhi. People talk about communal harmony, but when communal trouble starts, nobody even thinks about it . . . . Tempers are so high they don't stop even if you shoot at them," said Deputy Police Commissioner Deepak Swaroop as he stood in a rubble-littered intersection directing his forces.

The violence has spread to the neighboring state of Madhya Pradesh, forcing the closure of schools in both states, and opponents of the government's attempts to raise university and job quotas for lower castes and other depressed social classes have vowed to turn the protest nationwide.

"I'm more worried now than in 1981," said Swaroop, referring to quota riots four years ago, when scores died in arson and violence. "Definitely, this situation can spread. It has interstate implications." he added.

In Gujarat, the disturbances followed the state government's decision in January to raise the quotas for "backward classes" in professional colleges and government service from 10 percent of the openings to 28 percent in an effort to move closer to the group's 35 percent proportion of the state's population. The so-called backward classes comprise a mixture of castes that have been deemed to be economically and socially deprived.

That quota, which the government calls a "reservation," was on top of a 14 percent quota for members of remote tribal communities and a 7 percent quota for members of "scheduled castes," or Harijans.

Harijan -- which in Hindi means God's children -- is the term coined by Mahatma Gandhi for members of the Shudra caste, the lowest in the Hindu caste system, which consists primarily of manual laborers and landless farmers. The Harijan community, in turn, is divided into thousands of subcastes, including the Chandalas, or Untouchables.

Although many social barriers for Harijans have fallen in the cities, Chandalas in remote villages still frequently are regarded as outcastes and barred access to public wells or prohibited from eating with members of castes. Originally, the Chandalas' occupations were primarily in public sanitation and handling corpses.

In the nearly 2,000-year-old Hindu social code, the four principal castes are: Brahmin (priests), Kshatriya (warriors and kings), Vaishya (traders) and Shudra (manual laborers).

Taken together, 49 percent of professional college seats and government jobs in Gujarat were reserved for lower castes, tribals and "backward" classes, although the government has postponed implementation of the quotas. Madhya Pradesh recently increased its reserved quotas for those classes to 78 percent, despite a Supreme Court ruling that such quotas should not exceed 49 percent.

Opponents of the quota system in both states, who call themselves "antireservationists," say the increases were announced before last month's state assembly elections to attract votes from members of the lower castes and tribal communities, who together constitute a majority of the electorate.

"We know the government has to support the scheduled castes economically, but this is a gimmick for votes. The reservation should be reduced instead of increased. The scheduled caste fellow will go first and get admission before me. But if I'm better, I should go first," said Rajash M. Dave, a 20-year-old medical student who was arrested Tuesday along with 400 other protesters for defying a ban on public assembly and held for eight hours in a police cricket stadium.

In interviews at the stadium, the mostly young, upper caste protesters complained of reverse discrimination because of a quota system that they said has gotten out of hand and is subject to abuse. They said many lower caste families have transcended social barriers to become reasonably affluent, but their children still are automatically admitted to professional schools on the basis of the quota policy.

"The poor Harijans aren't getting the [college] seats. The rich Harijans are getting them, and with low [scholastic] averages. The reservations should be on economic lines, not on caste lines," said Ravinder Patel, 21, a medical school student.

Gujarat's chief minister, Madhavsinh Solanki, denied in an interview that the quota increase was politically motivated and timed for the elections. He charged that opposition parties were fueling the protest in an attempt to weaken the Congress (I) Party state government.

He said that the rightist Bharatiya Janata Party, in concert with Hindu supremacists of the Rashtriya Swayamsevak Sang militia, seized upon the quota controversy to instigate clashes between Hindus and Moslems.

Indeed, many of the recent clashes in the Walled City have been between Hindu and Moslem communities. Fighting between the two groups is commonplace in Ahmedabad.

But other clashes between youths and security forces clearly stem from anger over the reservation system. Numerous protesters interviewed described themselves as antireservationists and said their participation in the rioting had nothing to do with Hindu-Moslem tension.

Solanki, citing a statement by Prime Minister Rajiv Gandhi, said that while the quotas for scheduled castes and tribal communities were not negotiable, the government was prepared to negotiate on the quotas for the so-called backward classes.

"The states should take measures to ameliorate the conditions of the scheduled castes. I'm not a Harijan, but I espouse the cause of Harijans. I take it objectively as a function of the government to do that," said Solanki, a member of the Kshatriya caste whose daughter is married to a Brahmin and son to a Patel of the Vaishya, or trader, caste.

Gujarat's leading Harijan activist, Romesh Chandra Parmar, agreed with Solanki's view of government responsibility to the deprived castes, but argued that the responsibility extends further.

Parmar, state president of a movement called Dalit Panthers, or oppressed panthers, loosely fashioned after the Black Panthers of the 1960s in the United States, said, "If you want to change society, you have to do it economically, socially, culturally and educationally. We haven't even started."

"Casteism is an evil that has spread to all fields of Indian life -- politics, business, education and social relationships. It has its roots in thousands of years, and I can't envision that it will go away in my life. It is a very sad thing, but we must struggle. We must continue to fight," said Parmar