What was going on when I was born?

Four of the nation's largest banks yesterday announced reductions of a full percentage point in their prime lending rates, to 12 percent, the lowest level in more than two years. Other leading banks indicated that they expected to follow the move today, or later this week, and many bankers predicted that interest rates on consumer loans would also decline soon. Some mortgage rates, for example, were lowered yesterday and others are expected to drop today. The moves marked an acceleration of the trend toward lower interest rates, which began in August and was given impetus last week when the Federal Reserve apparently eased its monetary policy.

An article in Sports Pages yesterday incorrectly identified the general manager of the St. Louis Cardinals baseball team. He is Joe McDonald.

The Lenin Shipyard here was struck by workers today for a second day, and fierce street battles broke out again in the streets between riot policemen and workers demanding the restoration of the outlawed trade union Solidarity. Poland's martial-law Government reacted by ordering the shipyard ''militarized.'' This means that the workers, in effect, are now soldiers subject to military orders and discipline. If they press their strike Wednesday for a third day, they could be court-martialed or even shot. (Some workers said on leaving the shipyard that they had been discharged for striking, according to The Associated Press, and others said that they had been told to report to army enlistment boards.)

''I want harmony and unity in the party. Now the party needs a new system under a new leader.

fire orienteering technique,'' said Dick Murphy, giving no hint that his tongue was set firmly in cheek. ''Just walk straight through the forest till you hit water - then make a right.'' Mr. Murphy is one of about 175,000 Americans who brave the woods in all weathers in the fall and spring to practice an increasingly popular sport that involves, in primitive terms, getting from here to there without getting lost. Or, perhaps, without getting totally lost. The sport is orienteering, finding one's way with map and compass through a stretch of unknown territory to a predetermined destination. It is practiced in both national forests and city parks, by men and women, by children and golden-agers, and by enthusiasts who range from elite competitors to families on nature hikes who find comfort in the presence of the family dog. Orienteering has grown dramatically in America since it began to catch on in the early 1970's. Membership has increased 1,750 percent since the national organization, the United States Orienteering Federation, was founded in 1971, a leap from 200 to 3,500 members. There are now 56 local chapters in 26 states.

The abrupt decline of short-term interest rates in recent days, apparently the mainspring of the stock market rally, is being cheered by Administration officials who hope that it portends a smaller budget deficit. Lower interest rates reduce the cost of carrying the Federal debt, which is now above $1,000 billion. More significantly, officials say, they are necessary for a stronger economy, which would do far more to shrink the deficit by producing additional tax revenues and reduced outlays for unemployment benefits.

Four gunmen opened fire on two armored-truck guards outside a Bronx milk plant yesterday, killing one guard and seriously wounding the other and a bystander, the police said. The robbers, who had been sitting in a car, ambushed the guards with automatic weapons - probably submachine guns - shortly after 4 P.M. as the guards carried two money bags from the plant to an armored truck parked nearby, the police said. They said the gunmen continued to fire at one of the guards as he lay fatally wounded on the sidewalk. Deputy Chief Francis M. Sullivan, the commanding officer of detectives in the Bronx, said the holdup men escaped with about $65,000 in cash and checks.

It seems an astounding prediction: In five years, A.T.& T. could have less than 50 percent of the long-distance telephone market that it had dominated for so long. Last February, when an American Telephone and Telegraph Company official made that forecast in Congressional testimony, competitors dismissed it as an attempt to prevent stricter regulation of the company. But while some industry executives and analysts think Bell's forecast is too dire, they say that it clearly points in the right direction. A.T.& T. is losing its share in the long-distance market and losing it at accelerating rates. That trend is expected to continue as the long-distance market enters a period of intense competition and regulatory turmoil tied to the divestiture of the A.T.& T. operating companies.

''WHAT a dinner! I don't call it a dinner: I call it a meal,'' snorts a character in George Bernard Shaw's ''Heartbreak House'' as he emerges from a casually cooked, fitfully attended repast in the odd English country manor where the play takes place. Shaw sees the disintegration of dinner as yet another example of the decline of the English upper classes at the time of World War I. Conversely, throughout our literature, an enthusiastic commitment to the common partaking of good food at the end of the day has been consistently associated with cultural health. Most traditional comedies, for example, after putting their characters through the turmoil of forbidden romances and false identities, conclude on the regenerative note of a marriage and a communal feast. Even as dark a work as ''The Iliad'' ends with old Priam and young Achilles weeping by the torn body of Hector and then sitting down together to share a midnight leg of lamb in order to reassert and celebrate their common humanity. More than 2,000 years after Homer, across the Atlantic, most Americans are still making some attempt to knit together the different strands of the day over an evening meal, despite all the unraveling tendencies of contemporary American life.

The Milwaukee Brewers opened the 79th World Series tonight with a 17-hit offense and a dazzling three-hit pitching performance by Mike Caldwell that devastated the St. Louis Cardinals, 10-0. It was the most one-sided shutout in the World Series since 1960, when Whitey Ford of the New York Yankees defeated the Pittsburgh Pirates, 12-0, three games after beating them, 10-0. And it was the most one-sided opening game in history except for 1959, when Early Wynn and Gerry Staley of the Chicago White Sox combined to beat the Los Angeles Dodgers, 11-0. It was also a night of record-setting achievement by the Brewers, who won the American League pennant by sweeping three games from the California Angels after losing the first two. They mauled four pitchers, they hit in every inning but one, Paul Molitor became the first player in Series history to get five hits in one game, Robin Yount added four and Ted Simmons clipped his former teammates for a home run.

New York City and United Nations officials are exploring plans to build two 27-story residential towers on city-owned land along the East River to house the families of foreign diplomats and others. Gillian M. Sorensen, New York City Commissioner for the United Nations and the Consular Corps, said the site of the proposed housing was a narrow, unused strip of property between 36th and 38th Streets. With the aim of winning the backing of residents, who have voiced vigorous opposition, city officials and the United Nations Development Corporation are proposing the construction of a public promenade extending along the river from 36th to 51st Street. Half for Diplomatic Corps Half of the 400 units to go up on the site, now strewn with rubble, would be for United Nations staff or diplomatic families and half would be for tenants with no United Nations connection. Designed for middle-income families, the studios and one- to three-bedroom apartments would be priced in the prevailing range of rentals.

Lieut. Gov. Mario M. Cuomo said yesterday that, if elected Governor next month, he would ''use all the powers of my office'' to persuade the Legislature to enact a cap on the state budget, with the savings going to reduce taxes and rebuild crumbling public works. The Democratic-Liberal nominee for Governor made the statement in a 46-page report on his ''priorities and directions for economic development in New York State.'' Mr. Cuomo and his aides made it clear that the main purpose of the report was to provide a contrast to the 49-page ''Program for Job Growth and Tax Reduction'' released last week by Mr. Cuomo's Republican-Conservative opponent, Lewis E. Lehrman. Mr. Lehrman proposed invigorating the economy through a 40 percent cut in income taxes by 1991. He has been on television in recent days offering to send a copy of his report to anyone who wants to read it.