MANILA, AUG. 24 -- Police fired shots into the air and used water cannons to disperse demonstrators blocking a highway, as striking drivers protesting higher fuel prices crippled public transport in four provinces today.

Leaders of the country's largest left-wing labor union announced a nationwide general strike set for Wednesday to protest higher fuel prices.

The government's decision to increase fuel prices by about 20 percent has sparked the broadest public protests of President Corazon Aquino's 18-month rule. A strike by drivers of jeepneys, the Philippines' colorful minibuses, last week crippled transport in several areas of Manila and in some outlying provinces.

Condemnation of the government action, which took effect 10 days ago, has spread beyond Aquino's critics on the left, to include leaders of the Trade Union Congress of the Philippines, the nation's largest moderate labor federation, and even ruling party members of Congress.

Aquino approved the higher prices, which went into effect at midnight Aug. 14, saying the measure was necessary because of the depletion of the government's fuel subsidy fund. The fund had been used to keep fuel prices artificially low. The average price per gallon now is about $1.66.

Senior government officials said the price increase was approved by the president and Cabinet members in March, but delayed because of crucial May legislative elections.

Ruling party members in the Senate and House of Representatives have announced their intention to open public inquiries into the decision to increase prices.

The fuel price increase has also supplied Aquino's left-wing critics, many of whom are sympathetic to communist guerrillas fighting in the countryside, with a new opportunity to chip away at the president's popularity. Since suffering a crushing defeat in the May elections, left-wing groups sympathetic to the communist guerrillas have groped for an issue to galvanize opposition to Aquino's rule.

Analysts regard Wednesday's planned general strike as a key test of the radical left's ability to mobilize mass protests against the Aquino government. Radical leftist students today canceled a planned protest march to the presidential palace when they failed to attract enough people.

Two truckloads of demonstrators were arrested today in the central Philippine city of Cebu for blocking a road as protests against higher fuel prices spread, authorities reported. Police fired shots into the air and used water cannons in an effort to disperse hundreds of demonstrators, authorities said.

Witnesses told Reuter news agency that one policeman was wounded by a homemade bomb after police charged the workers, who had refused to clear the road.

A strike by drivers of buses and jeepneys paralyzed public transportation in four provinces of the Bicol Peninsula region southeast of Manila, the state-run Philippine News Agency reported. The agency also said a transport strike in Davao, a major seaport 600 miles south of Manila, crippled public transportation.

It appears unlikely that Aquino will bow to public pressure and roll back prices. Referring to the depleted subsidy fund, she told reporters yesterday that she did not see how prices could possibly be rolled back.

Leto Villar, a spokesman for the May First Movement, a radical left-wing labor organization, said members would launch a nationwide strike Wednesday. The group claims a membership of 650,000, although independent analysts believe the actual figure is closer to 200,000.