Disregarding appeals for order by the newly installed prime minister, Rajiv Gandhi, rampaging mobs of Hindus vowing revenge for the assassination of Indira Gandhi burned scores of Sikh-owned stores and houses here today as troops were called out in the capital and elsewhere in India.

Heavy black smoke hung over large areas of central New Delhi in the city's worst sectarian rioting since postindependence Hindu-Moslem violence. A stunned nation paid homage to the slain prime minister, who was gunned down yesterday by two Sikh security guards as she left her home.

As the unofficial death toll climbed, with estimates varying from 24 to nearly 150, troops were called out in 10 cities and towns and curfews were imposed in parts of the capital and in two dozen localities across the country.

Authorities issued shoot-on-sight orders here against persons involved in arson and looting. Meanwhile, gangs of Hindus roamed through New Delhi and adjacent old Delhi attacking Sikh temples, looting and burning Sikh homes and businesses, and pulling terrified Sikhs from cars and buses and beating them before setting fire to the vehicles.

Although paramilitary security forces and Army troops were deployed thinly through the city, they did little to intervene in the worst of the rampages as Sikhs sought sanctuary in temples or went into hiding.

Rajiv Gandhi, the 40-year-old son of the assassinated prime minister, issued "very strict instructions" to security forces and intelligence agencies to curtail mounting violence "at all costs," Home Secretary Madan M.K. Wali said at a press conference tonight.

But Wali conceded that the security forces were "probably overextended" in the capital and that Army troops were needed to restore order.

Wali and other Indian officials refused to comment on the investigation into the two suspected assassins of the prime minister. Although there were some conflicting reports, most accounts agreed that Gandhi was killed by two Sikhs who worked as security guards at her residence, and that both were killed or fatally wounded by Tibetan border police commandos immediately after the assassination. Officials also refused to say whether a wider conspiracy was suspected.

However, police in Punjab today rounded up eight persons, including six relatives of Satwant Singh, one of the two guards who reportedly shot the prime minister. Police said they arrested the guard's father, three brothers and two sisters, as well as a former classmate and another friend.

Satwant Singh, a police constable posted outside Gandhi's house, and Delhi police subinspector Beant Singh were shot and apparently killed minutes after they had opened fire on the prime minister with a Sten gun and revolver, riddling her body with 16 bullets.

Police sources said that Satwant Singh only recently had reported for duty after going on leave in his village in Punjab, and authorities said they were attempting to determine whether he had been in touch with Sikh separatist guerrillas still at large in the strife-torn northern Indian state.

Government sources said that Gandhi had insisted on retaining Sikh bodyguards on her security staff even after she had received death threats from Sikh extremists following the Indian Army's assault in June on the Sikhs' holiest shrine, the Golden Temple complex in Amritsar, in which 600 to 1,000 Sikhs were killed.

Meanwhile, almost all of the top opposition party leaders tonight pledged their full support for the new prime minister in curtailing violence. Following an hour-long meeting among Rajiv Gandhi, four Cabinet ministers and opposition leaders, a joint appeal was issued urging people "of all persuasions, particularly the active political workers and public servants, to exert themselves to the utmost and restore sanity and harmony."

"The nation's unity and integrity must be safeguarded at all costs and this is the utmost responsibility of every citizen," the statement said.

Rajiv Gandhi also ordered all chief ministers of Indian states who had come to New Delhi for Saturday's funeral to return to their state capitals and restore order, Reuter reported.

Convoys of troops with jeep-mounted heavy machine guns and recoilless rifles fanned out through New Delhi's trouble spots tonight, but rioting and arson continued in some areas despite localized curfews.

The worst hit areas were the white-colonnaded Connaught Circus shopping district in central New Delhi, the historic Chandi Chowk bazaar in old Delhi and the Karol Bagh district that lies between the modern capital and the old city.

As shops, movie theaters, a hotel and other businesses burned out of control, ignored by an overtaxed fire department, tens of thousands of mourners filed past the flower-covered bier of Indira Gandhi to pay homage to one of the strongest and best known women leaders in the world.

Lining up for nearly a mile before the Teen Murti House, where Gandhi's father, former prime minister Jawaharlal Nehru, lived and died, the mourners reflected the grief and bitterness that has grown over the assassination of the leader many Indians called the "Mother of India."

Government spokesmen said that no consideration has been given to suspending the public viewing in the wake of the rioting, which began this morning as Cabinet officials, members of Parliament and other dignitaries led by Rajiv Gandhi went to the Teen Murti House.

Throughout New Delhi, Sikhs vanished from sight as truckloads of Hindu youths brandishing wooden staves and other crude weapons drove through nearly deserted streets, chanting Hindu nationalist slogans and searching for Sikhs identifiable by their turbans and unshorn hair. Not far from the Parliament building, one Sikh ran crying in terror as he was pursued by a mob of shouting Hindus with lathis, or cane batons commonly used by police. Some Hindus carried knives or spears as they looked for Sikhs.

Public transport, a business long dominated by Sikhs, ground to a halt as rows of Sikh-owned taxis burned at their stands and their drivers went into hiding.

At the Bangla Sahib Temple -- New Delhi's largest -- about 150 Sikhs, some armed with long swords, looked nervously across a low wall as groups of Hindu youths walked slowly by, some carrying cans of gasoline. The Sikhs said some youths had attempted to storm the temple -- scene of Sikh-police clashes following the storming of the Golden Temple in June -- but were driven back.

"The police are watching them the Hindus and not doing anything. The mob is roaming without any hitch and can do whatever they want," said Burbachan Singh, a Sikh taxi driver who said his house in Karol Bagh was stoned earlier in the day.

Nearby, at an Indian Oil Co. office building that houses the library of noted Sikh poet Bhai Vir Singh, a fire that police said was set by an anti-Sikh mob raged out of control as Hindu youths spoke openly of vengeance for Gandhi's death.

"You can't stop the sentiments of the people who are hurt by the murder of our prime minister. The fire is bad, but the killing of an innocent woman is bad too. The united Hindu people retaliate," said R.P. Sharma, a 27-year-old Hindu accountant.

A large crowd gathered to watch a Sikh-owned paint store in the Pahar Ganj neighborhood burn, and alleged eyewitnesses to the torching of the store said that three Sikh partners were dead inside. One youth said one of the Sikhs had fired on a crowd that attempted to loot the store, adding, "They should have stayed in their houses."

Hundreds of youths roamed through an adjacent street, smashing windows, looting stores and setting fire to cars as about a dozen policemen armed only with lathis watched nervously. A busload of armed Central Reserve police drove by without slowing down as the mob, barely noticing, continued looting.

In Connaught Circus, once the commercial showcase of colonial New Delhi, Praveen Nanda, manager of the Marina Hotel, watched his hotel burn out of control. "There are no fire trucks," he said. "There are no police in sight. It's stupid. This is the land of Mahatma Gandhi. It is not expected in India."

Nanda, a Hindu who said he had lived "in complete harmony" with Sikhs, said his four-star hotel caught fire when a Sikh shop next door was set ablaze.

Most of the shops looted and burned by the mobs that wandered through the concentric streets of the circular shopping district were those with the names of Sikh proprietors. Occasionally, policemen riding bicycles would pedal past a store being looted and burned, glance casually at the mob, smile nervously and continue on.

Some shopowners said there were too many fires for the police to handle. "This is going on in hundreds of places. What can they do?" asked B.M. Sethi, a travel agent.

When a mob of about 4,000 Hindus gathered outside the Rakab Ganj Sikh Temple near the Parliament building this morning and began stoning it, Sikhs inside opened fire until the police responded with about five rounds of rifle fire. The body of one victim, believed to be a Sikh, was set afire just outside the temple.

While New Delhi witnessed the worst of the violence in India today, there were reports of police firing at rioters in the Calcutta area, where local officials said 10 persons were killed, and deaths of Sikhs in the states of Bihar, Uttar Pradesh, Madhya Pradesh and Jammu-Kashmir, all in northern India. There were also reports of deaths in Tamil Nadu and Maharashtra, in southern India.

Cities and towns where incidents of violence were reported included Kanpur, Lucknow, Mathura, Benares, Patna and Rae Bareli in the north, Indore, Gwalior, Jabalpur and Sagar in central India, and Agartala in the east.

In an unconfirmed dispatch, the United News of India news agency said tonight that 12 passengers on a train from Gwalior, in Madhya Pradesh State, were killed by an angry mob at the Morena railway station on the border with Haryana State.

There were no details of the reported massacre, and officials here said they could not confirm the account.

Wali said that only 12 deaths had been confirmed throughout India, but the United News of India, compiling dispatches from its bureaus throughout the country, said at least 50 persons died today. The agency quoted authorities as estimating 24 victims.

Wali, calling the rioting the work of a "lunatic fringe," said, "We will not allow this situation to continue. I am confident that today will be the last day of these incidents."

Later in the evening, the United News of India said that 115 persons had been killed throughout the country, but there was no official confirmation of that figure. Another news agency, the Press Trust of India, estimated nearly 150 deaths.