Hillsdale College in southwestern Michigan, an institution nationally known for its teaching of conservative family values, was left stunned by the abrupt retirement Wednesday of its president and subsequent published reports today that he had an intimate relationship with his daughter-in-law before her suicide on campus last month.

George Roche III, in a letter released by the college's board of trustees, said that he had "no wish to continue." The board, in a companion statement, attributed the resignation to "the combined pressures of his personal health and private family life."

But the conservative weekly National Review, in its online edition today, presented a detailed account of what it said was a 19-year affair between Roche, 64, and Lissa Roche, 41, who was married to his son, George Roche IV, a history professor at the college. George Roche III has denied the affair.

Lissa Roche, who was found dead of a gunshot wound in the head in the campus arboretum on Oct. 17, was the managing editor of the Hillsdale College Press for 14 years. Police officials declined to comment on the reports of a relationship but said there appeared to be no indication of foul play.

The suicide has reverberated far beyond the small, 1,200-student college, 90 miles southwest of Detroit, and throughout the conservative movement because of the college's role in promoting conservative values as well as Roche's reputation as one of the country's leading conservative intellectuals and most prolific fund-raiser in the movement.

Under Roche's 28-year leadership, the independent private college's endowment has risen from $4 million to $172 million, even as it has refused to accept federal financial aid, which would force the school to comply with federal regulations.

The National Review, in a lengthy and detailed account of the alleged affair and the trustees' investigation of rumors of it, said one of its reporters, John J. Miller, had interviewed Roche's son and had seen a copy of his statement to the police. The National Review's publisher, William F. Buckley Jr., who has a close association with the college, could not be reached last night.

The online edition of the Review said Roche had "conducted a 19-year affair with his daughter-in-law, who was the mother of his grandson." The conservative publication said the "episode may also contain broader lessons for conservatism--especially about the wisdom of building institutions outside the liberal currents of the higher-education mainstream."

The Review said Roche began an intimate relationship with his son's wife in 1980, shortly after the younger Roche married Lissa Jackson, and that it continued until her suicide, which occurred about a month after the college president remarried. Roche had divorced his first wife in 1988.

The newspaper said when Roche's new wife, Mary Hagan, moved into his house, George IV and Lissa were asked to move out. It said that on Oct. 17--the day of the suicide--Lissa Roche became distraught when she learned that her father-in-law and his new wife had reconciled following marriage difficulties. During a visit to Roche in a hospital where he was being treated for a diabetic insulin reaction, she told her husband of the alleged affair.

The newspaper said that in a meeting of the board of trustees Wednesday, the college president vehemently denied having a sexual relationship with his daughter-in-law. He was quoted as saying he loved her and that she "got very, very confused."

While declining to discuss the circumstances of the suicide or Roche's private life, Hillsdale College officials on Thursday had a one-hour meeting with students and faculty to reaffirm the institution's family values. Donald Mossey, president of the board of trustees, was quoted by the Detroit Free Press as telling the gathering: "There's been so much talk going around that I'm sure you've been inundated with much rumor, innuendo and some fact. Each of you will have to reach your own conclusion."