A U.S. oil company executive kidnaped early last month by a little-known armed group was released here early this morning, reportedly after his family had made a ransom payment.

Kenneth S. Bishop, 57, the operations manager of Texas Petroleum, an affiliate of Texaco, was flown to the United States hours after his release by a group identifying itself as the People's Revolutionary Organization.

On arrival in Miami, The Associated Press reported, Bishop expressed joy on being freed after 38 days in captivity and then was driven away. A relative was quoted as saying the family paid a ransom of several hundred thousand dollars.

Bishop was kidnaped March 7 by three armed men and a woman who ambushed his car in a Bogota suburb as he was driving to work. Two Colombian bodyguards were killed by gunfire.

The kidnaping came at a time when the Colombian government is seeking to pacify the estimated 3,000 guerrillas active in the country with an amnesty program and negotiations. So far, the initiative by President Belisario Betancur has had only partial success. Colombia is the largest of the few South American countries with democratic governments.

About 240 guerrillas have turned themselves in since the amnesty took effect last November, and the leadership of the M-19 guerrilla organization, one of the major groups, announced the suspension of armed activities late last year. Other groups have rejected the peace measures, however, and continued violent operations.

A statement released by Bishop's family through Texas Petroleum said that Bishop was in good health. Married to a Colombian, Bishop has lived here for 25 years. Their four children live in the United States. Texas Petroleum, which refused to negotiate with Bishop's captors, did not disclose details of Bishop's release or the leftist organization's demands.

An informed source said Texaco had brought three security specialists to the country to work on the case and that a ransom payment was made last night. Reports here of the amount ranged up to $1 million.

Bishop is the fifth U.S. citizen kidnaped in Colombia since 1975 and the second executive of Texas Petroleum to be seized by leftists here. A Colombian executive of the company was kidnaped in 1979 and later killed, reportedly by members of M-19.

The most dramatic guerrilla operation here was the two-month occupation by the M-19 of the Dominican Republic Embassy in 1980, when the U.S. ambassador was among those held until negotiations resulted in removal of the rebels to Cuba.

This morning, a bomb exploded at the Honduran Embassy here and injured at least two persons, including the Honduran counsel in Bogota. Signs left at the embassy attributed the attack to the M-19, despite the professed halt in activity by that group, and connected the action to alleged Honduran aggression against the leftist government of Nicaragua.

In the first week of this year, 33 persons were abducted by armed Colombian groups, officials here said last month.

Two days after kidnaping Bishop, the People's Revolutionary Organization sent a photograph of the executive holding a flag emblazoned with the group's initials to Bogota newspapers. An accompanying message threatened that Bishop would be killed on March 29 if unspecified demands were not met. A family member reportedly then made contact.

Diplomats here said that little is known of the organization. The group is believed, however, to be responsible for the murder of a prominent Colombian woman found dead late last year, six months after being kidnaped. A flag with the group's initials was draped over her body.