What was going on when I was born?

Gen. Wojciech Jaruzelski tightened his control over Poland today with a sweeping shake-up in the Communist Party that included the demotion of the main challenger to his political power. Stefan Olszowski, an orthodox Marxist with a strong power base among party professionals, lost his post as party secretary responsible for propaganda and ideology. Mr. Olszowski retained his seat on the ruling Politburo, but political sources said his future responsibilities would probably be limited to a secondary role in foreign affairs. The shake-up, which included nine promotions to key party positions and four demotions, was the most extensive in the party since the declaration of martial law on Dec. 13. A bitter power struggle has reportedly been under way for the last several weeks.

The United States has sent a high-level message to China that it will proceed with co-production of F-5E fighter aircraft with Taiwan, well-placed Administration sources disclosed today. The sources said the Peking Government had protested the American decision. Some sources said that the American message was transmitted in a letter from President Reagan to the Chinese leadership delivered in Peking by Ambassador Arthur W. Hummel Jr. in the past week. But White House officials would not confirm that the American communication involved a presidential message.

The Rev. Sun Myung Moon was sentenced to an 18-month prison term yesterday for tax fraud and conspiracy to obstruct justice, but he remained free pending an appeal. Sitting slightly slumped in a chair, with his hands folded in his lap, the leader of the Unification Church displayed no emotion as Judge Gerard L. Goettel sentenced him in Federal District Court in Manhattan. His lawyers said later that they were confident the conviction would be overturned. Mr. Moon, who would be eligible for parole after serving one-third of the sentence, was also fined the maximum of $25,000 plus the costs of prosecution. And he could face deportation proceedings.

The Labor Department proposed today to expand the hours and the types of jobs that 14-@ and 15-year-olds are allowed to work. The revisions would be the first substantial changes in child labor regulations in more than four decades. Labor Secretary Raymond J. Donovan said the proposal was intended to increase employment for young people. But Lane Kirkland, president of the A.F.L.-C.I.O., said, ''I would not have thought that even this Administration would do that.''

The Reagan Administration is holding up a shipment of cluster-bomb artillery shells to Israel while pressing the Begin Government for a report on its use of American-made cluster bombs in Lebanon, senior Administration officials said today. A cluster bomb carries a cannister of explosive pellets that spread over a large area. Cluster-bomb artillery shells work on the same principle but are fired from howitzers rather than dropped from planes. Although some Israeli officials have denied that cluster bombs were used in Lebanon, Congressional and Administration sources said that a Central Intelligence Agency report has found that Israeli forces did use cluster bombs in populated areas, causing civilian casualties.

With Iranian and Iraqi troops locked in heavy fighting just inside southern Iraq, the United States offered today to hold joint military exercises with Saudi Arabia and other Persian Gulf countries that might feel threatened by the conflict. No such exercises are currently planned, however, Reagan Administration officials said, and there have been no requests from Persian Gulf countries for the deployment of American troops in the area to help them defend themselves. The officials said the exercises, if planned, would primarily serve as a symbolic show of strength and American support for friends in the region. At the same time, a senior State Department official expressed ''deep concern about the air and sea strike capability of Iran against Gulf countries.'' Speaking at a press briefing arranged by the department on the condition that the official would not be identified, he said the United States was also concerned about the potential political unrest that a ''militarily predominant'' Iran could cause in the region.

The retired chairman of the Lockheed Aircraft Corporation, his wife and their elderly housekeeper were shot to death Thursday night in their secluded mansion here. Courtlandt S. Gross, 77 years old, and his wife, the former Alexandra Van Rensselaer Devereux, 72, were found today in the kitchen of the house on a winding, tree-shaded lane near this Main Line village, about 15 miles from Philadelphia. The housekeeper, Catherine Vander Veur, 69, was in a bedroom. They were apparently slain in the night by one or more intruders, according to the sparse details the police disclosed. The estate is in a neighborhood of wooded hills and valleys where large, well-kept homes on spacious lots are set among hedge-screened estates, accessible generally only from long driveways leading from narrow, tree-lined lanes.

Nicaragua said today that rightists helped by the Central Intelligence Agency and evangelical sects working as a fifth column launched a ''silent invasion'' from Honduras 12 days ago. The leftists said today that 100 people had died in recent fighting in the northern provinces, which they said had been infiltrated by over 1,000 guerrillas. Deputy Interior Minister Luis Carrion told reporters today that guerrillas were still crossing the border ''with the logistical and tactical support of the C.I.A.'' Both Mr. Carrion and Interior Minister Tomas Borge denounced foreign religious sects working in Nicaragua as ''nests of counterrevolutionary activity.''

The Government of Prime Minister P.W. Botha is engaged in a growing legal and political dispute with the leader of the Zulus, the largest black ethnic group in South Africa. The issue is its decision to excise a fragment of the Zulu ''homeland'' and cede it to the neighboring kingdom of Swaziland. Twice in one week early this month, Chief Gatsha Buthelezi, who is head of government in the fragmented state called KwaZulu and leader of what is said to be the largest black political movement in the country, has successfully gone to the courts to block proclamations of the white central Government. The first proclamation, made under a law called the Black States Consitutions Act, removed from KwaZulu's jurisdiction a strip of territory called Ingwavuma that is wedged between Mozambique's southern border and Swaziland's southeastern corner. If the Government's plan to give Ingwavuma to Swaziland goes through as part of a larger transfer of land and population that also involves the Swazi ethnic homeland of KaNgwane, it would give the landlocked kingdom an outlet to the Indian Ocean.

Somalia said today that its troops routed an Ethiopian invasion, forcing the attackers to flee back across the disputed Ogaden region after 15 days of fighting. The claim conflicted with broadcasts by Somali rebels on Thursday that said Somali Government troops were defeated in two battles along the Ethiopian border this week and that fighting had been reported in six of Somalia's 15 provinces. Reports from local and foreign reporters taken to the front said the fighting appeared to be over.

Bolivia's military President, Gen. Celso Torrelio, has offered his resignation, two senior military commanders said today.

The International Monetary Fund approved an $85 million loan to El Salvador today after many months of debate within the international financial agency. The credit has been criticized by some members of Congress and foreign policy groups as questionable in view of the civil war in the Central American country. The Salvadoran Government could use the money for arms if it chose to do so. Tom Leddy, Deputy Assistant Secretary of the Treasury for International Monetary Affairs, explained that the funds were ''for general balance of payments purposes.'' He said the fund ''doesn't say you can't spend it on this or that.''