The first cold weather of autumn has produced shortages of heat and electricity across Serbia, raising public frustration and posing a potential threat to the rule of Yugoslav President Slobodan Milosevic.

Mandatory two-hour electricity blackouts were imposed this week in Belgrade, capital of both Serbia and Yugoslavia, Novi Sad and other cities. The most serious situation was in the eastern town of Bor, where the heating grid went down during a snowstorm.

The seasonal cold snap has coincided with fresh signs of hyperinflation and food shortages. Nightly street demonstrations staged by Milosevic's political opponents have all but fizzled out, but the government seems worried that further deprivations could ignite a mass uprising by a population that once enjoyed the highest living standards in Central and Eastern Europe.

Even in the capital, there are supply problems with meat, sugar and cooking oil. Prices are rising at the rate of more than 150 percent a year. The free market value of the Yugoslav currency, the dinar, has plummeted to less than one-third the official rate, prompting rumors of a pending devaluation.

Mladjan Dinkic, who heads a group of independent economists here, said that a key reason for the dinar's weakness is a lack of foreign currency reserves held by the Yugoslav central bank, which cannot intervene to prop up the dinar. Yugoslavia has been unable to accumulate foreign capital by selling off state companies because of an international ban on foreign investment, and efforts to collect some $3 billion in debts owed Belgrade by Iraq and Libya have been fruitless.

The government also may be printing dinars to destabilize the government of Montenegro--Serbia's tiny, disaffected partner in the Yugoslav federation. Its president, Milo Djukanovic, a former Milosevic protege who has become one his most bitter foes, has warned that Montenegro may establish an independent currency if the dinar's slide continues. That step would be seen as tantamount to a declaration of independence that could lead to the final breakup of Yugoslavia.

In the past, Milosevic has shored up his political support by ensuring cheap fuel and food through lavish state subsidies. But with its financial reserves almost depleted, Belgrade is coping with the twin curses of shortages and soaring prices by blaming NATO's bombing campaign this spring and a panoply of international sanctions that have been in place for much of this decade.

"People will eventually get fed up with this regime, but it is still hard to say when that point will be reached," said Goran Pitic, a prominent economist. "For now, they still have enough resources to make life tolerable. But there is a lot of dissatisfaction, and any number of things could set off a popular revolt."

Pitic said, however, that he believes Milosevic has bought himself more time by appealing to the Serbs' time-honored sense of victimhood in faulting the outside world for his government's economic failures.

At a meeting Tuesday with U.S. and European diplomats in the Serb-controlled part of neighboring Bosnia, leaders of Serbia's pro-democracy opposition urged the early removal of international sanctions by arguing that punitive measures, such as a ban on commercial air travel, were playing into Milosevic's hands.

The United States has refused to lift any sanctions or offer any economic aid to Serbia as long as Milosevic remains in office. But some European countries are becoming uncomfortable with a strategy of economic pressure that, instead of forcing Milosevic from power, has put his political opponents on the defensive.

Over U.S. objections, European Union foreign ministers last week approved $5 million in fuel oil aid for Nis and Pirot, two opposition-controlled Serbian cities in which oil refineries were destroyed during NATO's 78-day bombing campaign.

Germany and France want to provide humanitarian aid and lift the air travel ban; Austria says it is ready to repair some Danube River bridges damaged by NATO airstrikes, the debris from which is blocking commercial water traffic.

Hungary, which is concerned about the fate of ethnic Hungarians living in the north Serbian province of Vojvodina, says that for humanitarian reasons it is now willing to allow Russian gas shipments to Serbia pass through its territory. But the Budapest government has sought assurances that Belgrade will pay about $20 million in overdue debts.

While the Milosevic government strives to blame Serbia's economic woes on opponents at home and abroad, there are indications that its own confidence is cracking. There has been renewed repression of dissidents, and educators say there has been a major purge of university professors who backed anti-Milosevic demonstrations.

In addition, the government is bracing the public for difficult times. Slobodan Petrovic, director of the Serbian power company, appealed to all consumers to curtail use of electricity as much as possible this month so that rationing could be avoided. He asked Belgrade residents in particular to find alternative sources of heat for their homes.