One hour before he was killed yesterday, Philippine opposition leader Benigno Aquino Jr. discussed his possible assassination with reporters aboard the flight returning him home from self-imposed exile.

"Assassinations serve a purpose," he told them. "I have to suffer with my people."

Aquino, 50, a former Philippine senator who opposed President Ferdinand Marcos, left the Philippines in 1980 after being sentenced to death and spending eight years in prison for subversion. He immigrated with his family to the United States.

He was permitted to come to the United States for coronary bypass surgery on the condition that he return to imprisonment in the Philippines. Instead, he decided to remain, saying, "A pact with the devil is no pact at all."

For the past three years he had been a research scholar, first at the Harvard Center for International Studies, then for the past year ending June 30 at the Massachusetts Institute of Technology Center for International Studies.

His widow, Corazon, and their five children, ages 12 to 25, are in Massachusetts, having planned to follow Aquino later. Yesterday they were packing to return to Manila for Aquino's funeral.

"He knew the risks he was running," Amelia Leiss, associate director of the MIT international studies program, said yesterday. "He thought they were worth taking. He felt he could be a rallying point for the democratic forces in the country. He was a deeply patriotic man."

At MIT, Aquino had studied the role of the military in developing countries.

Dr. Benjamin Brown, retired director of the Harvard Center for International Studies, said Aquino had studied "peaceful transition from dictatorship to democracy" there.

Aquino had done no major writing at Harvard, Brown said, because "He was preoccupied with what was happening in his country . . . . He stayed in touch with everybody . . . . He met and talked to everybody who could conceivably help him understand the Philippines."

Mrs. Aquino yesterday said she and her husband knew his life was threatened. "You always think of risks," she said, "but I never thought it would go this far."

Aquino's chief aide in the United States, Ernesto Maceda, himself a former Philippine opposition senator, said Aquino had considered returning home surreptitiously as recently as last week, but chose to go back openly so that he would not disappoint supporters waiting to greet him.

"He was aware of all the preparations being made for his arrival, so he preferred" an open return, Maceda said.

Maceda last week said Aquino's decision to return home despite Philippine government warnings about assassination plots was "irreversible."

"He would lose all his credibility if he doesn't go home," Maceda said.

Aquino left Boston Aug. 13, but his family and friends had not disclosed his whereabouts as he traveled.

"All I know is that my husband lived his life according to his beliefs and principles," Mrs. Aquino said. "He did not want to compromise . . . . His belief was his country should have a free press and democracy."

Mrs. Aquino thanked the people she had met in this country for their kindness.

"We have spent a happy three years here," she said, "in sharp contrast to the years my husband spent in prison."

Aquino's son, Benigno Aquino III, 20, greeting friends as they came to pay their respects, said justice will prevail. "Eventually, the truth will come out. My father was fond of saying, 'There's no such thing as a secret in Manila.' "

He said his father would have wanted to die in the Philippines.

"My father said if he was going to die, he wanted to die in his homeland . . . . No matter what happens, justice will be served."