ISLAMABAD, PAKISTAN, OCT. 23 -- India's powerful Hindu revivalists delivered a strong shock to Prime Minister V. P. Singh today by withdrawing support from his minority government, a move that could force Singh from office or lead to snap elections.

The Bharatiya Janata Party (BJP), a well-organized party of Hindu activists that is now the third largest in India's divided Parliament, announced its break with the prime minister after BJP leader L. K. Advani was arrested for leading a controversial religious march through northern India.

The move leaves Singh without a parliamentary majority and with no obvious means of securing one. But the prime minister said he would not resign and wished to test his strength in a confidence motion on the floor of Parliament, a vote that could take place within two weeks.

The decision about when or whether to schedule such a vote rests with President Ramaswamy Venkataraman, who met with Singh and Congress Party opposition leader Rajiv Gandhi. Venkataraman reportedly said that he would require some time to study the legal and constitutional aspects of the crisis.

In a statement, the BJP said it had left the coalition "because of the multiple failures of the government . . . and the provocative action of arresting Mr. L. K. Advani."

Singh's centrist Janata Party took power 11 months ago, propped up in Parliament by support from Communists on the left and the BJP on the right. The unwieldy alliance took shape after voters repudiated former prime minister Gandhi in national elections last November.

Given the fractiousness of India's politics and the sharp tensions raised in recent weeks by a caste conflict that cuts across party lines, the possible outcomes of the crisis are multitudinous, according to analysts in New Delhi.

Singh might cobble together a fresh majority by engineering splits in his opposition or by patching things up with the BJP. Communist leaders pledged support to the prime minister today, providing Singh with a base to build on. But leftist support alone will not keep his government in power.

The BJP's defection could also trigger renewed infighting in Singh's own Janata Party that could lead to his replacement as national leader without elections. Or, if Singh is defeated in a parliamentary confidence vote, Gandhi could be asked to attempt to form a new government under Congress leadership.

A break between the religious-minded BJP and Singh's secular Janata Party was widely seen as inevitable, since the two parties have virtually opposite views on the fundamental issue of the roles of church and state in India.

But the timing of the rift comes as something of a surprise, since neither Singh nor BJP leader Advani is seen as politically strong enough to win a parliamentary majority if new elections are held. The Congress Party, which has governed India for most of its years of independence, also appears to be weakened because of infighting in its ranks and challenges to its political identity posed by Singh's recent appeals to lower castes and the BJP's appeals to Hindu activists.

Singh, who is rapidly shedding his reputation as a timid consensus politician, appears to have gambled that the identity he built during the 1989 campaign as a clean and moral politician will sustain him through the present crisis.

In interviews during the last 11 months, Singh has talked frequently about his willingness to sacrifice his office on issues of principle in order to build a long-term political base. But only recently has he acted boldly on his own, initiating in August a controversial affirmative-action plan to set aside jobs for lower castes and then challenging Advani this month.

In a nationally televised speech Monday night, Singh tried to frame in broad terms his conflict with the BJP and his attitude toward the caste conflict that has rocked India in recent weeks. "The country is passing through a grim crisis," he said. "It is not a question of saving the government, but saving the country."

The immediate cause of the break between Singh and the BJP was an escalating confrontation over a plan by the BJP and other Hindu activists to construct a Hindu temple on the site of an existing Moslem mosque, called the Babri Masjid, in the northern Indian town of Ayodya.

The Ayodya controversy has flared from time to time during the past 40 years, most recently last fall, when Hindu revivalists sparked religious riots across India by threatening to tear down the city's mosque. Hindu activists say the Babri Masjid was built during the 17th century on the site of an ancient Hindu temple, a claim sharply disputed by scholars. But the facts of the case have been submerged in political opportunism and religious hatred between India's Hindu majority and its Moslem minority of 100 million.

In an apparent effort to build on the BJP's growing political strength in the populous north, Advani last month initiated a long chariot march toward Ayodya with the stated aim of starting construction of a Hindu temple there. As fears rose that the march could spark violence, Singh's government ordered the arrest of a reported 20,000 Hindu activists, seized control of the mosque and surrounded it with soldiers.

After Advani still refused to call off his procession, he was arrested by Bihar State's Janata Party government early this morning.