SANTIAGO, Chile (AP) _ The army's 62-year-old chief of protocol, released in a cold rain after four days in the hands of leftist guerrilla kidnappers, was under treatment in a hospital Friday for high blood pressure.

The abductors freed Col. Mario Haeberle late Thursday after driving him to a residential section of Santiago. Relatives said Haeberle arrived home and then went to the army hospital to have a heart ailment checked.

''He is basically well, but his blood pressure is high,'' said a son who answered the phone at the colonel's home but wouldn't give his name. ''My father is still shaken up over what happened.''

Seven gunmen of the communist-led Manuel Rodriguez Patriotic Front, which is waging an armed campaign against military rule in Chile, seized Haeberle from his driveway at home Monday morning and eluded a citywide search by thousands of police and soldiers.

It was the second abduction by the three-year-old urban guerrilla group to publicize its battle against President Augusto Pinochet, the army commander who seized power in a 1973 coup and insists on ruling at least until 1989.

The group, which takes its name from a Chilean independence hero, held a paramilitary policeman for two days before freeing him unharmed last April.

Haeberle wrote to his wife during captivity that he was handcuffed and treated like a prisoner but not tortured. He said he became nauseous for lack of prescribed pills for a heart ailment.

In a statement telephoned to news agencies, the rebels said they freed Haeberle in response to an appeal by Cardinal Juan Francisco Fresno, the Roman Catholic archibishop of Santiago, and because the kidnapping had achieved its propaganda purposes.

Pinochet called the kidnapping part of a psychological campaign by Marxist enemies. His government barred Chilean news media from reporting it except for official communiques.