July 3, 1990

LEAD: As expressions like dirty rat, rat's nest, rat race and smell a rat suggest, the rat may be people's least favorite creature. But the few scientists who are studying it express nothing but admiration for the rat's instincts, ingenuity and tenacity.

LEAD: Southern California, perhaps more than any other region, offers a clear test of the American economy's capacity to convert from military to peaceful purposes.

LEAD: Ralph McA. Ingersoll 2d, who aggressively acquired newspapers in this country over the last decade but has been under mounting financial pressure, left the newspaper business in the United States yesterday to run newspapers in Europe.

LEAD: The idea had long lingered in William O'Keefe's mind, but it didn't take shape until three years ago, shortly after he found his dented and decapitated mailbox lying along a country road. Why not build an indestructible mailbox? Mr. O'Keefe, a service manager for a local oil company, had already lost seven mailboxes to vandalism.

LEAD: Forstmann Little & Company announced yesterday that it had agreed to buy the General Instrument Corporation, a leading supplier to the cable television industry, for $44.50 a share, or $1.6 billion.

LEAD: Companies

LEAD: The new president of Philips N.V. announced today that the Dutch electronics giant would take a $1.44 billion charge against earnings and eliminate about 10,000 jobs in Europe as part of an effort to revive its loss-ridden computer and electronic-components divisions.

LEAD: Acting swiftly to capitalize on last week's Federal court ruling giving copyright protection to the set of computer commands used in its popular 1-2-3 spreadsheet program, the Lotus Development Corporation sued two California software companies yesterday, accusing them of copyright infringement.

LEAD: Mayor David N. Dinkins yesterday named a black woman to the remaining seat on the Board of Education, completing a board whose ethnic diversity reflects the school system's largely black and Hispanic population.

LEAD: SCIENTISTS have discovered a hereditary factor that greatly increases susceptibility to the chronic arthritis that can change Lyme disease from an almost unnoticeable ailment to an affliction lasting several years.

LEAD: East Germans took their new West German marks for a trial spin today, hunting through stores newly stocked with Western goods, but for now they appeared mostly to be just looking.

LEAD: Fireworks 9:20 P.M. on the East River. F.D.R Drive will be closed for viewing from 14th to 42d streets from 7 P.M. until after midnight. NEW YORK Government offices: Federal, state and municipal all closed. Post office: Express Mail and special delivery only; main post office open at 33d Street and Eighth Avenue.