What was going on when I was born?

By the end of the decade, the United States steel industry will be far smaller and more concentrated, with more efficient plants more widely dispersed throughout the country producing specialized products better keyed to the individual needs of its customers. This was the picture that emerged yesterday from interviews with a variety of economists and industry analysts. They described an industry finally shaken from its historic torpor, closing inefficient plants and embarking on a wave of consolidation that it is hoped will cut its labor costs and make it more closely competitive with its international rivals. Only last September, the Republic Steel Corporation, the nation's fourth- largest steel producer, announced that it would merge with the Jones & Laughlin Steel Corporation, a subsidiary of the LTV Corporation and the nation's third-largest producer. Last December, the United States Steel Corporation, the nation's largest steel producer, announced the closing of three of its major plants and parts of more than a dozen others, eliminating 15,430 jobs.

Orders for manufactured goods from factories rose 1 percent in December and a strong 10.6 percent for 1983, the biggest jump in four years, the Commerce Department said today. The department also revised its report of last week on orders for durable goods - products expected to last three years or more. This sector gained two-tenths of 1 percent in December, revised from the earlier figure that showed a 1.1 percent decline.

The Business and the Law column on Jan. 24 incorrectly identified the Federal agency that approved an exchange of assets between Warner Communications and Chris-Craft Industries. It was the Federal Trade Commission.

The Nissan Motor Company, the maker of Datsun cars and trucks, agreed today to begin assembling cars here in 1986 in what would be the first such entry by a Japanese auto maker into the European Common Market. But the accord, which calls for Nissan to invest about $70 million in a kit- assembly plant capable of turning out some 24,000 cars a year, falls far short of earlier proposals. Nissan, which began talking with the British Government some three years ago, had at first envisioned setting up a full-scale manufacturing plant in Britain to produce 200,000 cars a year.

The veil of mystery that surrounds the Federal Reserve's monetary policy may become a little harder to see through under a new accounting procedure that begins today. The change, which affects the way banks account for their reserves, is intended to give the Fed tighter control over the growth of M-1, the closely watched measure of money available for spending. Actual results may be different, however, since Fed officials have been saying since October 1982 that they are setting monetary policy less according to changes in M-1 and more according to what happens with inflation and the economy as a whole. In the credit markets, analysts are grinding their teeth because the change could make short-term rates more volatile and make it harder to predict money supply changes and to interpret Federal Reserve policy.

Democratic leaders in Congress today derided President Reagan's efforts to reduce the budget deficit as ''tokenism'' and said they would propose their own package of spending cuts and new revenue worth at least $200 billion over three years. That is double the deficit-reduction ''down payment'' suggested by the President in his State of the Union Message last week. Representative Jim Wright of Texas, the House majority leader, said the Democratic proposals would focus mainly on lower military spending and higher taxes, even though Mr. Reagan has expressed great reluctance to alter his budget in these areas. Mr. Wright also said the Democrats would recommend cuts in automatic benefit programs such as Social Security, which have generally been sacred to Democratic lawmakers. 'Bad News,' O'Neill Says Speaker Thomas P. O'Neill Jr. said in a statement, ''The Reagan budget message is bad news for the American people. Instead of getting serious about deficit reduction, the President has retained his title as the country's biggest budget-buster.''

Taxpayers who hope to write off medical expenses or casualty losses incurred last year may be disappointed to find they either do not qualify for the deduction or will receive a much smaller benefit than in the past. The deductions for unreimbursed medical expenses and personal casualty and theft losses were victims of a Congressional effort to trim the Federal deficit. The Tax Equity and Fiscal Responsibility Act of 1982 significantly tightened the eligibility requirements for these two deductions in a way that will also sharply reduce benefits for the taxpayers who do manage to qualify. Under the new rules, many individuals will be required to have hundreds of dollars more in medical and dental bills and thousands of dollars in additional unreimbursed casualty losses just to meet the minimum eligibility standards. A Closer Look at the List The changes will force individuals to rummage harder through the list of eligible expenses in hopes of coming up with enough to offset, at least partly, the stiffened requirements. It will also force many to review their insurance coverage since the Federal Government can no longer be counted on as a co-insurer. ''The answer used to be that the Government covered you, but those who have large deductibles had better rethink that,'' said Richard Shebairo, a partner at the accounting firm of Arthur Young & Company.

designer, began working on the renovation of a one-bedroom co-op apartment in a 1950's high-rise building in Manhattan. She kept a diary of the project from the day she got the job until the apartment was finished. ''People see slick photographs in shelter magazines, but they have no idea how the house or apartment got that way,'' said Miss Halperin, who began her own business eight years ago. The designer's client recalled: ''Having never been involved in a renovation before, we had no idea what an arduous, messy process it was. Now that it's over, I'm glad we stuck it out because the apartment is well designed.''

President Reagan today proposed a $925.5 billion budget for the fiscal year 1985 that calls on Congress to continue cutting domestic spending for the rest of the decade, to delay major tax increases and to move forward with a military buildup. ''All signs point to continued strong economic growth, vigorous investment, and rising productivity, without Text of the Budget Message, charts and related articles, pages B7-10. renewed inflation - all but one,'' the President wrote in his Budget Message to Congress. ''Only the threat of indefinitely prolonged budget deficits threatens the continuation of sustained noninflationary growth and prosperity,'' he said. ''It raises the specter of sharply higher interest rates, choked-off investment, renewed recession and rising unemployment.'' Little Gain on Deficit Despite this exhortation, the President tailored his budget to the election year and proposed modest spending reductions and a small package of tax increases that would result in a 1985 deficit of $180.4 billion, about $3 billion less than the deficit projected for the current year. Without these policy changes, and the President's decision not to seek $13 billion more in military increases that he had once planned, the deficit had been projected at $207.6 billion.

The Advertising column in Business Day on Tuesday included an erroneous identification by Young & Rubicam of Donald M. Casey's position there. He is director of business development worldwide.

Democratic legislators were accused by the White House of ''playing politics'' on the Lebanon issue and drafting a resolution that ''aids and abets'' enemies of peace in the Middle East. President Reagan's spokesman issued a strong denunciation of the House Democrats' resolution, which would call on Mr. Reagan to begin ''a prompt and orderly withdrawal'' of the American marines from Beirut. (Page A1, Column 6.) Deploring ''Sadat,'' a mini-series about the life of Egypt's assassinated leader, Egypt has banned all films produced or distributed by Columbia Pictures. Abdel Hamid Radwan, Egypt's Minister of Culture, reportedly charged that Columbia's docudrama, which appeared on American television, contained ''historical errors that distort the accomplishments of the Egyptian people.'' (A1:4-6.)

A brief report in Weekend on Jan. 27 about the exhibition ''The Precious Legacy: Judaic Treasures From the Czechoslovak State Collections'' gave an incorrect location. The show will be on view through March 18 at the Bass Museum of Art in Miami and will open April 15 at the Jewish Museum, Fifth Avenue and 92d Street.