Four persons were killed and at least 113 wounded today when bombs apparently planted by Basque separtists exploded in Madrid's two main railway stations and at the capital's airport.

The bombs exploded almost simultaneously shortly after 1 p.m. Madrid time, about half an hour after a caller claiming to represent ETA, the Basque terrorist organization, phoned Spain's national news agency EFE to say explosives had been placed at all three sites.

Police said there was not enough time to evacuate the three locations.

The bombings appeared to be part of a major offensive by the separatist group against the federal government, which only recently negotiated a home rule statute for the Basque provinces with moderate Basque politicians. The ETA, however, demands full independence.

When the blasts occurred, both train stations and the airport were crowded with passengers leaving for summer vacations.

The first bomb exploded at Barajas International Airport, killing one person and wounding at least nine others. Police said the injured included two American tourists, Eugene de Matteo, 63, of San Francisco, and his wife, Terese, 61, who were waiting to board a flight to San Francisco.

The other bombs exploded a few minutes later. Police said both the bomb at the airport and the one at the central Atocha railway station had been placed in luggage lockers. Two persons died and scores were wounded at the Atocha station.

Weeping passengers and relatives thronged the street in front of the station as police struggled to evacuate the wounded. Blood-soaked personal effects, twisted metal lockers and shattered glass strewed the station's main entrance.

At the modern Chamartin station in the north of the city, the explosion occurred near the ticket office. Barman Manuel Moreno, who was in the station's cafeteria 70 yards from the bomb, recalled a white flash and "a rumbling that seemed to go on forever."

"Then it was all screams, blood, and I saw police putting a blanket over a body," he said. A Danish woman tourist was killed at Chamartin station.

Police said later that the three bomb blasts wounded 113 persons, about 40 of them seriously.

For the past week there had been concern in Madrid that the agreement on home rule for the Basques would provoke violent reaction from ETA, a 10-year-old terrorist organization dedicated to achieving full independence for the region.

ETA is a Basque acronym for "Basque Homeland and Liberty." In their first move since the autonomy accord was reached, the terrorists yesterday ambushed paramilitary police patrols in the Basque area, killing three policemen and wounding four more. In attacks near Bilbao and in San Sebastian, three patrols were sprayed with bullets from machine pistols fired from speeding cars.

Today's bombings were seen as a continuation of the terrorist organization's offensive against the agreement.

The "military" wing of ETA announced last week its rejection of any compromise with the Madrid government, and vowed to continue its battle against the state.

At the same time, however, another ETA faction pledged to cease guerrilla operations and work for independence through political means, using the self-government provisions of the home-rule bill.

Informed sources here believe that a wedge has been driven between elements of the Basque separatist extremists, and that diehards in the movement's "military" faction are resorting to indiscriminate violence. CAPTION: Picture 1, A Basque terrorist bomb left this destruction in Madrid's airport yesterday. Three bombs killed four persons and wounded 113. AP; Picture 2, A badly injured victim of a bomb explosion at Madrid's Barajas Airport is taken to an infirmary. Four persons were killed in three blasts, AP