September 13, 1983

WHEN the opening bell rang at the 55th Street School in Milwaukee one day last week, Linda Martinez greeted her kindergarten class with the words, ''Como esta usted?'' Jonette Pickett and the 21 other 5-year-olds replied in unison, ''Muy bien, gracias,'' and when the teacher read out their names each one replied, ''Presente.'' Then they picked up their ''lapices'' and went to work. Jonette and his classmates all come from English-speaking homes, but they are going to school in Spanish as part of a special program designed to make them thoroughly bilingual by sixth grade. Immersion programs like the one at the 55th Street School are the exception, but they are indicative of a growing interest among parents, teachers and researchers across the country in starting to teach foreign languages at the primary school level.

President Reagan has authorized ''aggressive self-defense'' tactics to protect the Marines in Lebanon and is consulting with Congress on a resolution to approve a continuing American military presence there, Administration officials said today. The officials said ''aggressive tactics'' meant the use of naval planes and guns, if necessary, to protect the Marine force that has been under fire at Beirut's International Airport. In the consultations with Congress, James A. Baker 3d, the White House chief of staff, met today with the House Speaker, Thomas P. O'Neill Jr., to marshal support for a resolution. Mr. Baker was told the President should seek formal backing for American military involvement in Lebanon under the War Powers Resolution of 1973. O'Neill Warns the Syrians ''We want to work together with the White House,'' Speaker O'Neill said later. ''If Syria thinks America is divided and it can wait around until we pull out, they are wrong.''

SCIENTISTS who study biology at its most basic level are in the midst of a crescendo of new discoveries that seem to be unraveling of the mystery of the cancer process. In the last few months, they have added to the list of known human cancer genes, identified new significance in the breakage and rearrangement of chromosomes, begun to see the function of cancer genes' counterparts in the normal body, and identified a two-stage sequence in which two cancer genes of different classes act in step to produce a malignancy. So fast and furious is the pace of discovery that some experts say informally that more has probably been learned in the past few years than in the previous quarter century. ''With the new molecular tools, so many things are just coming together,'' said Dr. George F, Vande Woude of the National Cancer Institute, one of the experts in the field. Most of this increasing wealth of knowledge has to do with the genes, the basic hereditary messages carried in the form of DNA (deoxyribonucleic acid) in all living cells, and with the chromosomes, the tiny threadlike structures that carry those genes somewhat like beads on a string.

A report Friday in the Briefing column of the Washington Talk page gave incorrect information on obtaining the Almanac of American Politics, 1984 edition. It is available (by mail or in person) only at the Washington office of The National Journal, 1730 M Street N.W., Washington, D.C. 20036. The price is $35 for hardcover, $22.50 for paperback.

From the time Congress recessed last month until its return yesterday, New York's two Senators had remained hard at work, each in his own fashion. Daniel Patrick Moynihan was holed up in a former one-room schoolhouse near his farm at Pindars Corners in Delaware County, writing a book on such issues as Social Security and the MX missile. Alfonse M. D'Amato spent the recess as if he were running for re-election - now. His term will expire in 1986. He held news conferences and issued statements on credit-card fraud, lost revenue from state gasoline taxes, narcotics, the Long Island Lighting Company's Shoreham nuclear power plant, the tentative assignment of a naval force to New York Harbor, health care, and Federal loans to companies in the garment district.