April 11, 1988

LEAD: Hachette to Buy Grolier Hachette, France's top publisher, has arranged to buy Grolier, an American educational publisher, in a deal worth about $449 million. Page D1. Hijackers' New Threat A Kuwaiti jet's hijackers pledged to carry out a ''slow, quiet massacre'' of their hostages, but were persuaded to pull back on the threat.

LEAD: Another season of moral ambivalence will end this week when the tax deadline passes, and researchers are beginning to learn how that ambivalence mixes with opportunity and other factors to produce tax cheats.

LEAD: THE MEDIA BUSINESS Grolier has tentatively agreed to be acquired by Hachette, the companies said. Grolier's board is scheduled to meet today to consider the proposal of $24.25 a share in cash for the 95 percent of the company's common shares that Hachette does not already own. The deal's value would total about $449 million.

LEAD: New and rebuilt subway cars on New York City's oldest lines have raised the system's mechanical reliability to a level not seen by riders since before the city's fiscal crisis in the mid-1970's, according to the Transit Authority.

LEAD: Law enforcement specialists say corruption within the American criminal justice system is more widespread now than at any time since Prohibition because of the explosion in the power and profits of the multibillion-dollar illicit drug industry.