What was going on when I was born?

The chairman of a House subcommittee said yesterday that next Monday's hearing on allegations of police brutality against black New Yorkers would be held in a state armory in Harlem. Mayor Koch immediately responded that he would not attend. The Mayor said the ''cavernous atmosphere'' of the armory was not an appropriate place to hold a Congressional hearing. The hearing is a continuation of one that was aborted soon after it began last July 18 by a disturbance. Mr. Koch attended that brief session along with Police Commissioner Robert J. McGuire and was prepared to testify.

A senior Soviet official said today that it was ''wishful thinking'' for the West to hope that outrage over the shooting down of a South Korean airliner would prompt the Kremlin to make concessions in medium-range missile talks in Geneva. The official, Georgi M. Korniyenko, who is a First Deputy Foreign Minister, spoke at a news conference at which he and Marshal Sergei F. Akhromeyev, a first deputy chief of the General Staff, appeared to rule out compromises that might forestall or reduce planned missile deployment in Western Europe. Mr. Korniyenko also said demands for compensation for families of the airliner victims were ''irrelevant'' because financial and political responsibility for the destruction of the plane and the deaths of its 269 passengers and crew members rested with the United States, which he said had sent the civilian airliner on a spying mission. The news conference appeared intended to affirm the Soviet position in the face of the international outcry.

The nation's Big Three automobile manufacturers reported today that sales for the first 10 days of September were up 20 percent from very weak sales in the same period a year ago. Analysts expressed optimism for the the fourth quarter and for 1984. The three companies, the General Motors Corporation, the Ford Motor Company and the Chrysler Corporation sold 125,051 new cars, compared with 104,227 in the comparable period last year. There were eight selling days in the Sept. 1-10 period in 1983 and 1982.

Three radicals who said they were fighting for black liberation were convicted here today of murdering two policemen and a Brink's guard and stealing $1.6 million from an armored car in Rockland County nearly two years ago. The defendants - Kuwasi Balagoon, 36 years old; David J. Gilbert, 39, and Judith A. Clark, 33 - were each found guilty of all charges against them, three counts of second-degree murder and four of first-degree armed robbery. A jury of seven men and five women reached its verdict quickly. The jurors began deliberating at 11:37 A.M. and returned at 3:27 P.M. to render their unanimous verdict. During the deliberations they returned to the courtroom for 50 minutes, for a rereading of witesses' accounts of crime, which occurred Oct. 20, 1981.

Media General presents itself as a straight-arrow place where all employees and executives must subscribe yearly to the publishing, broadcasting and newsprint company's written code of business ethics. Thus, the allegations of income tax fraud, mail fraud and kickbacks at its subsidiary, the William B. Tanner Company of Memphis, have proved to be an embarrassing episode for Media General. ''Needless to say it was all very surprising to us,'' said Alan S. Donnahoe, Media General's longtime chief executive officer. Tanner Acquired Last Year The hometown newspaper company here has grown over the years into Media General, which has its roots in pre-Civil War newspapering. A conservative empire stretching far beyond its headquarters here, it had never encountered the image problems that the Tanner episode presented. The Tanner Company, which buys and sells broadcast time on a barter basis, was purchased last year by Media General for $39 million. Last month, 30 Federal agents descended on Tanner headquarters in Memphis seeking documents in connection with the allegations.

New York State must change its laws by Oct. 1 to allow heavier trailer trucks on interstate highways or it will lose $750 million in Federal highway money, transportation officials said today. New York is the only state that does not conform to Federal law, which requires that trucks up to 80,000 pounds be permitted on interstate highways. New York City excludes trucks heavier than 73,280 pounds, because they cause heavy wear on the roads. Legislative leaders have drafted legislation to overrule New York City and increase the weight of trucks on interstate highways. The legislation would also permit the double-trailer trucks known as tandems on interstate roads within the city's boundaries.

The Baldwin-United Corporation, under pressure from regulators to generate cash, said yesterday that it would put its MGIC Investment Corporation up for sale. Baldwin had purchased MGIC in 1982 for $1.2 billion, about half of which was borrowed. The burden of that debt has contributed heavily to Baldwin's problems. MGIC is the parent of the Mortgage Guaranty Insurance Corporation, the nation's largest mortgage insurer; the American Municipal Bond Assurance Corporation, which sells municipal bond insurance, and the MGIC Indemnity Corporation, which sells directors' and officers' liability insurance. Baldwin said that MGIC would be sold as a whole, or in pieces.

Fall apparel sales, often a barometer of the all-important Christmas season, have gotten off to a slow start. Consumer interest in colder-weather clothing has been hurt by hot temperatures in recent weeks, merchants say, resulting in reduced shopper traffic through apparel departments. While merchants hope that the slump will end with the coming of cooler weather, many say they have been left with heavier stocks than they prefer and some uncertainty about the fall season. The general industry tendency to push the fall season in August proved particularly difficult as temperatures remained in the mid-90's in most sections of the country. The apparel selling slowdown has continued even after Labor Day, when Americans traditionally begin buying most of their fall clothing.

The New York City subway system has 465 stations, 6,400 passenger cars and what seem like a million stairs. It is the stairs that keep people in wheelchairs from using the stations, boarding the trains and getting around the city underground. Groups representing the handicapped are trying to force the Metropolitan Transportation Authority to add elevators to make the subways accessible to those in wheelchairs. The M.T.A., however, has long argued that putting elevators in the 79-year-old system would be costly, difficult and maybe even dangerous. Newer subway systems in Washington and San Francisco that were built with elevators draw only a handful of wheelchair users, M.T.A. officials point out. But advocates for the handicapped argue that elevators in the larger New York system will attract a greater number of handicapped riders, both those in wheelchairs and those with canes, crutches or braces.

New York State yesterday approved a Consolidated Edison Company application to burn coal at two generating plants in the city that now use oil. The ruling by the Commissioner of Environmental Conservation, Henry G. Williams, came after several years of bitter controversy. It was hailed as a landmark decision by environmental groups, but condemned by Con Edison. The utility said the ruling's provisions were unduly restrictive and would prove to be so expensive that conversion might not be possible.

THERE is more and more talk of color in architecture and there is more and more talk of ornament in architecture - both of these elements yearned for, it would seem, as means of giving the buildings we make today something of the elan of the architecture of the past. If one material has always seemed able to yield both color and ornament - and, indeed, has been absolutely crucial to the architecture of the last hundred years - it is terra cotta, that baked clay that can be molded and fired into almost anything. Terra cotta is given its proper homage in ''Rhapsody in the Blue - Terra Cotta Skylines,'' an exhibition that has just opened at the Urban Center, 457 Madison Avenue (50th Street), where it will run through Oct. 26.

France's Socialist administration today proposed a surcharge of up to 8 percent on high-income taxpayers plus an increase in other taxes and social security charges, and it said the country faces another year of austerity. The moves, contained in the 1984 budget approved by the Cabinet this morning, are intended to hold the deficit on Government spending to 3 percent of the national economy's expected output. They are also aimed at carrying out President Francois Mitterrand's commitment to close France's big trade deficit by the end of next year and reduce its 9 percent inflation rate to 5 percent. Under the proposed budget, which must be approved by the Parliament, where the Socialists have a majority, Government spending is to rise 6.8 percent in 1984. That would be the smallest increase in 13 years.