MANILA, Philippines (AP) _ Former Finance Secretary Jaime Ongpin, among the most controversial and influential Cabinet members until his September removal, was found fatally shot today in what his son said appeared to be suicide.

Security guard Angelito Villacorta said he and a janitor found the body of the 49-year-old Harvard graduate slumped in the chair of his second-floor office after hearing a single gunshot about 3 p.m.

Police said Ongpin had a single bullet wound in his right temple and was slumped over clutching a .38-caliber pistol in his hand.

''My father's death is an apparent suicide,'' said Ongpin's eldest son, Rafael. ''He had been unhappy for some time following his end of tenure from the government when he resigned.''

Ongpin was relieved as finance secretary Sept. 16 in a Cabinet shakeup following the bloody Aug. 28 coup attempt, which elicited widespread criticism over rancor, policy differences and lack of coordination within President Corazon Aquino's administration.

Critics blamed Ongpin and Executive Secretary Joker Arroyo, who was also dropped in the shakeup, for much of the division that marked the first 19 months of the Aquino administration.

Ongpin and Central Bank Gov. Jose Fernandez came under fire for negotiating a debt rescheduling agreement, signed last July. Critics claimed the agreement committed the government to a repayment schedule that made it impossible to finance economic development.

The agreement stretches payments of about $10.3 billion in foreign debts over 17 years, including a 7 1/2 -year grace period.

Ongpin was the younger brother of Roberto Ongpin, who served as trade and industry minister under former President Ferdinand Marcos.

He graduated from Ateneo de Manila University in 1958 and from Harvard University Business School in 1962.

Ongpin became president of Benguet Corp., a major mining firm, in 1974.

After the 1983 assassination of Mrs. Aquino's husband, former Sen. Benigno Aquino Jr., he demanded economic reform in the Marcos administration.

Ongpin campaigned for Mrs. Aquino in the disputed 1986 presidential election and was appointed to the Cabinet when Mrs. Aquino took power in the February 1986 civilian-military coup that ousted Marcos.

In a statement today, Mrs. Aquino called Ongpin ''an outstanding Filipino who had the courage of his convictions.''

''He fought the dictatorship during the martial law years when few would do so,'' Mrs. Aquino said. ''Jimmy was also a superb technocract and organizer whose contribution to my presidential campaign was priceless.''

Ongpin's successor and ally, Vicente Jayme, told reporters he met with his predecessor last week and saw no evidence of depression.

Ongpin was survived by his wife, Marybelle, three sons and two daughters.