September 23, 1986

TWO giant concrete spheres on railroad tracks, open to the sky to collect starlight in two mirrors more than 40 feet apart, forms the heart of an unconventional observatory that is overcoming longstanding limits on the sharpness of telescope images. On a rock-strewn plateau above treeline in the foothills of the French Alps, the prototype observatory has succeeded in combining the pair of light beams with the sensitivity needed to see stars as actual disks. Many astronomers in Europe and the United States believe the technique - known as optical interferometry - is the most promising way to resolve the fine details of stars, star clusters and other objects that current telescopes can see only as points of light. By giving a second dimension to the stars, astronomers hope to learn more about how they form and how they organize themselves into clusters and galaxies. On nearby stars, surface features such as sunspots may come into view for the first time, giving invaluable clues to stars' internal dynamics.

The summerlong drama over interest rates, the dollar and the course of the world economy shifts this week to Washington, where promises that countries would devise a better way to run the economy are now in doubt. The annual meetings of the 151-member International Monetary Fund and its sister institution, the World Bank, which start Thursday and run through Oct. 3, mark a high point of the economic calendar. This year the sessions are coming at a critical time. The world economy is afflicted by a myriad of problems that have proved stubbornly resistant to solution. Lopsided trade is favoring Japan and West Germany and undermining American productivity. Slow growth in the United States is dragging down the debt-ridden countries of Latin America. Interest rates worldwide remain uncommonly high for a period of low inflation, stifling the growth prospects of all countries.

The Federal trial of Stanley M. Friedman, the Bronx Democratic leader, and four other defendants opened here today with the judge telling potential jurors that there was ''not going to be much dispute that there was corruption in the Parking Violations Bureau.'' The judge, Whitman Knapp, addressing the people who will hear New York's most important corruption trial in decades, said they would have to address the Government's contention that ''each of these defendants willfully and knowingly participated'' in what the Government said was a racketeering enterprise. With a half-hour explanation of the purpose of juries, and then the most elementary details of a case that has held many New Yorkers in thrall for months but has apparently barely scratched public consciousness here, Judge Knapp began the first major trial to stem from the scandal that has rattled New York City for months. The 10-count indictment charges the defendants with racketeering, bribery, receiving bribes and mail fraud.

The space agency is moving forward on modifications of the shuttle's booster rockets amid rising concerns that it may be discarding more reliable designs in an effort to save time and hundreds of millions of dollars. The focal point of the criticism is the agency's quiet decision in recent months to reject, at least for now, design changes that would require scrapping 72 giant steel rocket casings ordered six months before the space shuttle Challenger blew up on Jan. 28, killing its crew of seven. That decision has prompted serious questions about whether the program for repairing the rocket's flaws permits engineers to build in the best possible margin of safety, especially in light of discoveries made since the Challenger disaster. Apprehension on Pressures Meanwhile, there is growing apprehension among some involved in the shuttle redesign. ''Everything is schedule, schedule, schedule,'' one senior engineer at Morton Thiokol Inc., which makes the rockets, said last week, complaining that new ideas for ways of sealing joints on the rockets were being dismissed. ''There is a lot of frustration that we don't have time to do the job right,'' said the engineer, who insisted on anonymity.

With its ''witching hour'' problems over and interest rates dipping a bit, Wall Street yesterday staged its most potent rally in more than two weeks. Investors, who have jettisoned stocks they considered unattractive in an environment of rising interest rates, yesterday actively bid up the price of those same shares. The result was a sizable gain for most market indicators, including a 30.80-point jump in the Dow Jones industrial average, to 1,793.45. ''I think it's the absence of fear,'' said Robert Stovall of Stovall 21st Advisers Inc. in explaining the improvement. He added that investors were no longer worried that they were ''going to get whacked by some options-related programs.''