March 17, 1992

International The Japanese stock market improved marginally today amid a tense atmosphere. Analysts said most players appeared to be watching for what, if anything, the Government would do to try to arrest the steady erosion in investor confidence. [ Page D1. ] Companies Robert J. Eaton, who was named to replace Lee A. Iacocca when the chairman and chief executive of Chrysler retires at the end of the year, gives up a 29-year career at General Motors and takes his biggest risk yet in joining the No. 3 U.S. auto maker. [ D1. ]

EVER since the virus that causes AIDS was discovered, scientists have puzzled over a central mystery of the disease. How can this virus smolder in the immune system for as long as 10 years before it finally destroys a person's ability to fight infections? What is going on in that prolonged period of steady, but very subtle, decline of the immune system? After years of bafflement, investigators now believe they have nearly cracked the puzzle. They have several competing ideas to explain the mystery, and some researchers propose that all the mechanisms they are finding may act in concert to topple the immune system.

On a hill behind this mile-and-a-half-high city, this year's most awaited marathon runners are training on the steep slopes and flat stretches, dodging donkeys laden with straw and weaving among women whose backs are piled with wood. On one crisp morning recently, Abebe Mekonnen, the 1989 Boston Marathon champion, led a pack of elite runners who were striding through five leisurely laps, a little over four miles apiece. Negash Dube, last year's Beijing Marathon winner, gave the more seasoned Abebe a deferential edge as they finished their weekly endurance workout.

By giving up a career at General Motors after 29 years to succeed Lee A. Iacocca as Chrysler's chairman, Robert J. Eaton is taking the biggest risk yet in a career marked by calculated chances. Most recently, the chief of G.M. Europe delivered sizable profits to bolster G.M.'s ailing domestic operations and quickly pushed the auto maker into new manufacturing and sales operations in Poland and Hungary, where G.M. introduced its first car last week.

NEW YORK CITY GAY GROUP LOSES ON IRISH PARADE A Federal judge refused to order a group of gay marchers admitted to the St. Patrick's Day Parade, putting to rest several months of legal wrangling but setting the stage for possible confrontations at the traditional festivities today. The decision also forced politicians to choose whether to march at what had always been one of the city's premier political events. A1. A QUANDARY IN QUEENS Since the early 1960's, a constant feature of life in Flushing, Queens, has been the smell of freshly baked bread wafting out of the Taystee Bakery. Soon, though, the bakery will be shut down, posing a classic problem for the Dinkins administration. How far should it go to subsidize manufacturers so that there are reasonable-paying jobs for unskilled, uneducated workers, many of whom are immigrants or minorities? A1.