JAKARTA, Indonesia - Riot police fired tear gas today at thousands of rock-throwing students demonstrating on the eve of drastic fuel price increases, which Indonesia's president defended as the only way to stave off an economic crisis.

Security forces chased down about 100 demonstrators in the center of Jakarta, hitting some with sticks, after the youths set tires ablaze, vandalized a bus and exchanged a volley of rocks with police on a busy street near their campus.

"Anarchy will only deter investment," said President Susilo Bambang Yudhoyono, who has made the unpopular decision to raise the price of gasoline, diesel fuel and kerosene sharply. The size of the increase was to be announced later today, but ministers said the cost of many fuel products could climb by as much as 50 percent.

That would push up the price of everything from rice to cigarettes in the sprawling country of 220 million people, half of whom live on less than $2 per day.

The price increases follow Yudhoyono's decision to slash fuel subsidies that have helped protect Indonesia's poorest from spiraling global prices for years, but also threatened to blow the cash-strapped government's budget.

Last year, the government doled out $7.4 billion for the subsidies - more than the international community has pledged on rebuilding efforts in countries hit by last year's tsunami.

"I realize that this is not a popular policy, a bitter pill that we have to swallow, but we have to do it to save the nation's budget and the future of the country," Yudhoyono said.