Gunmen believed to be militant Sikhs hijacked a bus in rural Punjab early this morning, separated out Hindus aboard the vehicle and killed 14 of them in the bloodiest episode of the latest upsurge of violence in the predominantly Sikh state, police and government officials reported today.

According to initial reports from Chandigarh, four masked gunmen aboard a rural bus forced the driver to stop near the village of Lubaniawalai in the southwestern Faridkot district shortly before dawn.

The gunmen separated Sikhs from Hindus, then opened fire on the 21 Hindus. Thirteen were killed outright and another died on the way to the hospital. Officials said two of the wounded were in critical condition.

The incident sent shock waves through the country, which has grown increasingly apprehensive about Sikh demands for a homeland as militants have turned their campaign into violent attacks on Hindus in recent months.

A solution to the Punjab violence has eluded Indian Prime Minister Rajiv Gandhi's government, which managed to overcome several other long-running disputes with minority groups in other parts of the country. It was just a year ago yesterday that Gandhi claimed success in reaching an accord ostensibly resolving the Punjab dispute, only to see it unravel amid hostile splits within the Sikh political community.

As the incidents have grown more violent, there have been increasing calls for Gandhi to intervene with greater force to rout the Sikh militants, who are referred to as terrorists by the government and much of the press.

Several thousand Hindus have fled their villages in recent weeks for safe havens outside the Punjab, and others have been moving from isolated villages to cities and towns where there are greater concentrations of Hindus.

Today's incident prompted statements of outrage from across the political spectrum and Home Minister Buta Singh rushed to the area. Major political parties in the Punjab called for a protest strike today in response to the killings.

Punjab Chief Minister Surjit Singh Barnala called the deaths an "outrage against humanity and all civilized norms" and his Cabinet called upon Sikhs in Punjab not to be trapped by those who "wanted to throw the state into a fratricidal bloodshed."

Punjab has been in turmoil for the better part of the 1980s as militant Sikhs have pressed their demands for an independent homeland or, at a minimum, a large measure of autonomy and control over the state, which is 60 percent Sikh. In the most violent incident to date, more than a thousand Sikhs and soldiers were killed when the Army routed well-armed militants from the Golden Temple in Amritsar in June 1984.

Up until recent months, however, most of the violence has involved either Sikhs against government forces or Sikhs against Sikhs, as bitterly divided factions fought for ascendancy. Recent months have seen the shift to Sikh-Hindu clashes as Hindu groups have responded to the attacks of the Sikhs.

Gandhi's strategy appears to be to try to leave Punjab's affairs in the hands of the Sikhs themselves, hoping that relative moderates such as Barnala can salvage a political accord.

The central government has strengthened the paramilitary forces it has sent to the Punjab. The troops have been sweeping through suspected militant hideouts and sanctuaries over the past couple of weeks claiming the capture or death of several militant leaders and the taking of large caches of arms.

Today's incident appeared to be a response by the militants to the sweeps, demonstrating that they still are in action.

An opposition spokesman in New Delhi, Atal Bihari Vajpayee, of the Indian People's Party, told Parliament today the extremists had "chosen to attack at a time and place of their choice when the government was busy patting its back for having made them run for life."

Barnala also has been under increasing pressure from dissident factions of the major Sikh party, the Akali Dal. Parkash Singh Bardal, a former chief minister and Barnal's main foe within the established parties, sharply criticized him yesterday, saying his government "no longer represents the aspirations of the Sikh people."