June 13, 1986

Platinum prices posted strong, fresh increases yesterday, as traders bid up prices in response to unrest in South Africa, where much of the precious metal is mined. In active trading on the New York Mercantile Exchange, the July platinum contract jumped $10.20 an ounce yesterday, to $454.20, just below a three-year high of $455.50 that was struck earlier this year. South Africa produces 80 percent of the platinum coming from the non-Communist world. About 60 percent of the strategically sensitive metal goes to industrial use, 30 percent to jewelry and 10 percent for investment, dealers say.

A new Soviet arms proposal may have figured in President Reagan's apparent move Wednesday to shade, but not to alter, his decision to disavow the strategic arms limitation treaty of 1979, according to Administration officials. The Soviet offer entails dropping the requirement that the United States reduce its so-called forward-based systems, meaning American fighter-bombers based in Western Europe and on aircraft carriers, but would raise the proposed limit on overall strategic nuclear forces to 8,000, from 6,000, the officials said. The new offer is also said to permit long-range sea-launched cruise missiles rather than banning them as before. These missiles would then be counted in the total of 8,000 nuclear bombs and missile warheads. This contrasts with the proposed American ceiling of 6,000 ballistic missile warheads and air-launched cruise missiles only. Mindful of Soviet Offer Officials said Mr. Reagan was mindful of this offer in his comments Wednesday and wished to avoid fouling the atmosphere created by the new proposal, presented in Geneva earlier in the day. The officials also said Mr. Reagan might have wanted to mollify Western European leaders who expressed disapproval of his decision May 27 to abandon the 1979 treaty.

To Carl Guardino, owner of the Sea King Sea Food Market here, the problem of East-West trade barriers is no longer simply the stuff of international summits. Mr. Gzardino has taken a decidedly microeconomic approach to the issue: to sell seafood to his increasingly Oriental clientele, he has posted the Japanese names of all the fish he stocks. ''I can also say, 'Thank you very much' in Japanese and 'What else do you want?' '' Mr. Guardino said. To Sara Small's third-grade class, the Far East does not seem too exotic anymore. Among the 18 students in the class at the Greenvale Elementary School in Eastchester, two are from Korea, five from Japan, one from China and another from Thailand.

NEW YORK CITY, the birthplace of Tin Pan Alley, the home of Broadway and one of America's two main centers of broadcasting, can still lay claim to being the pop-musical capital of America, even though commercial pop music diversified dramatically after the rise of rock-and-roll. Though the city is not first in everything pop - Nashville owns country music, and Los Angeles outdoes New York in television and movie music -New York remains the country's foremost musical melting pot, stirring together American, Afro-Caribbean, European, Latin American and dozens of other musical vocabularies. Almost every kind of pop music thrives in the New York area. This evening, for instance, the adventurous pop-jazz explorer could see the Brazilian pop crooner Roberto Carlos at Radio City Music Hall at 8 o'clock, then journey downtown to Jazztrack (27 Barrow Street) to catch an infrequent appearance by the saxophonist and composer Sam Rivers and his trio at 11, then sample smart new-wave rock by the Feelies at Danceteria (30 West 21st Street) at 2 A.M. That is three totally different musical worlds in less than eight hours.

Friday -DIORAMA OF DREAMS -''The work is about urban life,'' Brookie Maxwell says of her 50-foot diorama ''42d Street: A Walk Across Twelve Blocks of Continuous Sculpture.'' ''42d Street'' is a three-dimensional representation of 12 actual blocks of 42d Street - complete with the Public Library, Theater Row, and even some movie houses. ''I've grown up in New York City and the people of this city are my people,'' Miss Maxwell said. ''If I convey a message in my art, it is, 'Have courage, hold on to your dreams.' If that's coming through in my work, then I'm successful.'' ''42d Street'' is now on exhibit at the School of Visual Arts, 209 East 23d Street; gallery hours are 9 A.M. to 8 P.M. Monday through Friday. Admission is free. Information: 679-7350. Saturday FOSSIL FREE-FOR-ALL In past years, visitors have brought in walrus teeth, the jaw bone of a whale, 100 million-year-old fish fossils, even an extinct cousin of the lobster, perfectly preserved. Saturday from 1 to 5 P.M., you may bring anything that intrigues you to the Museum of Natural History, Central Park West at 79th Street, for identification by museum experts. All objects - old or new, animal, vegetable or mineral - will be examined, although scientists will not identify gemstones and no appraisals or estimates of monetary value will be made. The museum established Identification Day in 1979 as a response to the large number of requests from the public for information about items collected every-GOG jump where from Staten Island to Sri Lanka.