January 7, 1986

The Postmaster General was replaced today after only a year in the job. The official, Paul N. Carlin, will be succeeded by Albert V. Casey, according to Postal Service spokesmen. Mr. Casey, 66 years old, retired as the chairman and president of American Airlines last February. The Postal Service board of governors met here in closed session today to act on the transition. John R. McKean, the board chairman, scheduled a news conference Tuesday morning to make the announcement.

Ronald O. Perelman is a betting man. When Pantry Pride purchased Revlon Inc. last November for $1.9 billion, Mr. Perelman, Pantry Pride's chief, rejected a $900 million offer from Adler & Shaykin, an investment company, to buy Revlon's beauty business. The $900 million question now is whether Mr. Perelman can return to that business some of its previous luster. It is a risky wager. While Revlon still commands the biggest share of anyone in the retail cosmetics industry, its name is no longer regarded with the same reverence by store buyers or cosmetics customers, and that has hurt the company: Sales for the beauty products division over the last five years have been flat, and operating profits have fallen.

On New Year's Eve, when Rich Reddick heard that his younger brother Marcus had been taken to the hospital with a firefighting injury, he did not believe it could be serious. Marcus Reddick was 26 years old, so young, so nimble - he used to slide down the fire station pole upside down. The Reddick brothers joined the Newark Fire Department together seven years ago, during a minority recruiting drive, and by all accounts they were doing better than all right. In his free time, Marcus had nearly completed an engineering degree; Rich was on the list for captain.

''The links between international terrorism and Libya are clear. Any effort by the Qaddafi regime to portray itself as somehow backing away from its earlier positions is disingenuous at best.

Even as the space shuttle program struggles to overcome nagging troubles, scientists are laying plans for a bold new era of space transportation meant to go far beyond the shuttle's achievements, and even beyond problem-laden rocketry itself. The goal, a vision of the 21st century, is to slash the cost of moving people and freight into space. The machines for this endeavor have such futuristic names as Sky Hook, Launch Loop and Star Bridge. What makes them unusual is that they are meant to operate not by directing the force of chemical explosions but by tapping the kinetic energy of the earth, the planets and objects in motion about them. According to aerospace experts, cheap transport based on such principles would greatly speed man's conquest of the heavens. The feasibility of some of these principles will be tested for the first time in 1988 when a space shuttle unreels a 62-mile-long cable with a satellite tethered to its end. Later, longer ''tow lines'' might provide power to speed space vehicles about the solar system.