May 25, 1983

Trafalgar House P.L.C., the real estate and construction company that owns the Cunard Line, bid more than $450 million today for control of the Peninsular & Oriental Steam Navigation Company, one of the world's oldest and best-known shipping companies. P & O's directors immediately rejected the offer, calling it ''derisory and in no way reflecting the earnings potential of P & O or the strength of its underlying assets.'' Many analysts in the City of London agreed.

IT may be hard to believe, but the summer season really starts this weekend. Beach and country houses are officially opened, guest lists are being drawn up, the barbecue grill is being cleaned, and parties and entertaining are on many minds. Nobody ever seems to have absolutely everything that's required to face the summer in style and comfort, so we've collected an assortment of the little things that can add to the fun. Some are supremely practical, others are a touch luxurious, but all were chosen because they are good looking as well as functional.

Two seminary presidents, each of whom has left a vivid personal imprint on his institution, are stepping down after writing celebrated but distinctly different chapters in theological education. James I. McCord, a robust native Texan whose deep raspy voice still has a trace of a drawl, is leaving his post on June 1 after 24 years as president of Princeton Theological Seminary in New Jersey. At the Princeton seminary, an independent institution founded in 1812, Mr. McCord has upheld and, in the opinion of many, strengthened a long tradition of cultivating a learned Presbyterian clergy for a largely prosperous, established church. On June 22, George W. Webber of the New York Theological Seminary, on West 29th Street, will officially end 14 years of shaping an innovative curriculum for mostly black and Hispanic students that is widely considered the country's boldest theological program. Mr. Webber, a shy, self-effacing minister of the United Church of Christ, brought the seminary back from near collapse. Different Aims and Styles Colleagues are lavish in their praises of both men. Dr. John W. Beeners, a member of the faculty at the Princeton seminary, said of Mr. McCord: ''He is a cultivated, sophisticated, strong leader. I think he's even a greater pastor and friend than an administrator.''

RMINDA du PONT served caviar, tenderloin of beef salad and marinated mushrooms with Dom Perignon from the trunk of a brown Rolls-Royce. Blair Both had a cold three-layered mousse of tomatoes, chicken and sorrel along with cream of asparagus soup. She kept them cool in the shade of a 1934 Buick - complete with rumble seat - that had belonged to Louise du Pont Crowninshield. Susan Fraley and several friends wore straw garden-party hats and served their cooperative tailgate picnic on a table covered with a Madeira cutwork cloth. Such elegance was in evidence on a recent warm, breezy day at the Winterthur Museum and Gardens near Wilmington, Del., where hundreds of tailgate picnics dotted the gently rolling grounds. It was the sort of spring day that has unfortunately been in short supply, when the white and pale-pink blossoms on the dogwoods shimmer in the sunlight, the deep-red flowers of the azaleas are in full bloom and a large, inviting greensward seems the ideal place to dine. As luxurious as the food and surroundings seemed, however, most of these dishes were not prepared by professional chefs but by home cooks who simply like to cook and to picnic.

The Supreme Court ruled today, 8 to 1, that racially discriminatory private schools are ineligible for Federal tax exemptions. In an opinion by Chief Justice Warren E. Burger, the Court said there was no question that the Internal Revenue Service was correct when, in 1970, it stopped granting tax-exempt status to discriminatory schools. President Reagan sought last year to revoke the 1970 policy because, he said, it had ''no basis in law,'' in that there was no specific ban written in the revenue service code. This action came to symbolize his Administration's break with the civil rights policies of the recent past.