NEW DELHI, JULY 7 (TUESDAY) -- Sikh gunmen killed at least 38 passengers and wounded 32 aboard a bus in Punjab State late last night, according to Indian news agency reports quoting police.

The toll was the highest in a series of such attacks against Hindus and raised a major challenge to the government of Prime Minister Rajiv Gandhi, which took control of the state government two months ago.

According to reports from police, five gunmen stopped a crowded bus about 15 miles south of the Punjabi capital of Chandigarh, forced it into a nearby field and opened fire on passengers, most of whom were Hindus.

Twenty-four persons were killed by gunmen in a similar attack Nov. 30. In the first such incident a year ago, 14 persons died. Each of the earlier attacks led to extreme tension between Sikhs and Hindus elsewhere in India, and especially here in the capital, where several people were killed in clashes following the first bus massacre.

Sikh militants seeking an independent homeland in the predominantly Sikh Punjab have adopted a number of tactics to try to force Hindus out of the state and to create tensions elsewhere in the country that could force Sikhs to go to Punjab in search of security.

Police immediately sealed borders between Punjab and neighboring states and special security measures were expected in Delhi and other cities, where tension already has been running high due to clashes between Hindus and Moslems this summer.

Most of the victims of the latest attack reportedly were Hindus traveling to Rishikesh in Uttar Pradesh State, a major pilgrimage site for Hindus.

According to police officials, the bus, which belonged to the Haryana State Roadways Corp., was carrying about 70 people when it was forced to stop near the village of Lalru.

The attackers had followed the bus in a white car and a truck from Chandigarh, before commandeering it.

United News of India quoted a woman survivor as saying that one of the men pointed a revolver at the driver's neck, forcing him to leave his seat. "They drove the bus some distance before stopping it on the wayside," the woman identified as Kalawati, was quoted as saying. "I jumped out of the bus and hid in a paddy field . . . . We heard shooting continuing for quite some time."

According to Reuter news agency, another surrvivor told police that one of the gunmen said, "We are going to search and loot these people," and then just opened fire inside the bus.

The Associated Press quoted police as saying that one of the attackers was killed in the crossfire.

The other gunmen reportedly fled after the shooting and a man in a passing van discovered the scene when he heard the cries of the victims. He called police in Chandigarh.

Punjab Gov. S.S. Ray, who has administered the state since the central government took control on May 11, immediately went to the scene.

When the Gandhi's government abandoned its policy of relying on a Sikh government in Punjab, Home Minister Buta Singh, himself a Sikh, said, "If we had not intervened, it would have led to a civil war."

But, despite direct administration from New Delhi and tightened police efforts to curb the extremists, the killings have continued, with the toll now believed to be more than 500 for this year.

As a result of the violence, bus services in Punjab are suspended after 8:30 p.m., but that of Haryana State, which shares Chandigarh as its capital with Punjab, had continued to operate through the short stretch of southern Punjab.

The bus service reportedly had been considering placement of armed guards aboard its vehicles.