What was going on when I was born?

About 4,000 Peruvian Army troops are waging a campaign against 2,000 insurgents on the high mountain plateaus above this small town, but according to reports from the battle area it is mostly unarmed peasants who are dying. The army officially reports that 854 people, including about 600 guerrillas and only 50 Government troops, have died this year in the fighting, centered on Ayacucho Department or state, 250 miles southeast of Lima. But the toll is actually much higher according to senior military and police officers, sources close to the guerrillas and reports from the mountainside here. There is no way directly to confirm any of the reports. The army imposed secrecy in the zone when it opened an offensive against the insurgents. And the insurgents, members of a group known as Shining Path, shun all contact with reporters.

President Reagan indicated to top national security aides today that he would modify his proposal that the Soviet Union make deep cuts in long-range missiles, but continue to insist on a one-third reduction in missile warheads, according to Administration officials. The officials said it was their understanding that the President will propose a new limit for each side of about 1,200 deployed intercontinental-range missiles instead of his original ceiling of 850. This would be down from about 2,350 for Moscow and about 1,600 for Washington. At a National Security Council meeting this morning, the President thus adopted the basic arms control recommendation of his Commission on Strategic Forces, namely changing the negotiating emphasis from deep cuts in missiles to firm controls on missile warheads.

The chairman and chief executive of Norton Simon Inc., David J. Mahoney, will have to increase the bid he and a group of investors are making for the large consumer products company, analysts predicted yesterday. ''It seems to be a consensus on Wall Street that Mr. Mahoney will not get away with his rather low offer to Norton Simon shareholders,'' said Guy P. Wyser-Pratte, executive vice president and head of the arbitrage department at Prudential-Bache Securities. Under the proposal received by the board of directors Monday, shareholders would get about $21 a share for the company's 24,046,000 shares, plus eight-hundredreths of a share of $100 preferred stock valued by analysts at about $8.50, or a total of $738.8 million. With other money borrowed to pay debt and provide working capital, the total value of the buyout would be $1.65 billion.

Stock prices plunged yesterday, reflecting growing apprehension that the Federal Reserve might soon tighten its monetary policy, sending interest rates higher. The Dow Jones industrial average closed 19.33 points lower, at 1,194.91, after being off only slightly more than a point at noon. The drop was the Dow's largest since it fell 21.87 points on May 2, when Morgan Stanley, a leading investment firm, told clients it had switched from a bullish viewpoint to a cautious one concerning the market's short-term outlook. The New York Stock Exchange's composite index of 1,500 common stocks and the Standard & Poor's 500-stock index also finished lower yesterday. The composite index fell 1.03, to 94.37, while the 500-stock index dropped 2.06, to 162.77.

The Federal Court of Appeals here has ruled that New Jersey cannot regulate labor unions whose members work in the gambling casinos in Atlantic City. The decision, reached Monday by a three-judge panel, was a defeat for the state, which has been trying to screen the leadership of unions in Atlantic City in an effort to prevent the infiltration of organized-crime figures into the casino industry. The ruling came in a suit brought by the union as it sought to be freed from participating in state hearings. After a long investigation, the New Jersey Casino Control Commission found last year that the president and the grievance manager of the largest casino union were associates of Nicodemo Scarfo, the reputed leader of organized crime in Atlantic City, and other crime figures.

Three of 31 samples in preliminary tests taken in the area surrounding an abandonned herbicide plant here contain detectable levels of the toxic chemical dioxin, Governor Kean said tonight. The Governor, joined by Federal and state officials, stressed at a news conference at City Hall that the dioxin levels detected were extremely low, and that the findings did not suggest there was contamination ''at any significant level'' beyond the immediate site of the former Diamond Alkali Company, at 80 Lister Avenue in the Ironbound Section. In addition, Robert E. Hughey, the state's Commissioner of Environmental Protection, said the three samples were ''uncertified,'' and that the dioxin levels detected might be due to anomalies in the collection process.

The Money table in Business Day yesterday incorrectly reported the Federal funds rate. It reached a high yesterday of 8 7/8 percent and a low of 8 3/4, and closed at 8 7/8.

A Soviet official said today that more than 100 people died when a Soviet passenger ship rammed a railway bridge across the Volga River on Sunday night, ripping off the vessel's top deck. A spokesman for the Intourist travel organization said the vessel, the Aleksandr Suvorov, hit the bridge at the city of Ulyanovsk at about 10 P.M. Moscow time, when many of the passengers were in a salon on the upper deck watching a movie. He said that those who died were all Soviet citizens. The accident was the worst known inland waterway disaster in the Soviet Union since World War II.

The Senate today turned back by large majorities last-ditch efforts by conservatives to block an $8.4 billion increase in the American contribution to the International Monetary Fund. But after a daylong debate, the chamber put off until Wednesday a final vote on the legislation itself, sought by the Reagan Administration as part of a strategy to ease the world debt crisis. In today's principal action, 9 mainly liberal Democrats joined 17 mainly conservative Republicans to vote against a budget waiver for the bill.

Senator Frank R. Lautenberg, who built a personal fortune by founding the largest data-processing company in the nation, warned in his maiden speech in the Senate today that computers threatened to create a new class of poor people. The New Jersey Democrat said computers were proliferating more rapidly in homes and schools in wealthy districts, leaving the poor to become illiterate in the new technology. ''The concept of computer literacy defines a new type of illiteracy, and the potential for new and distressing divisions in our society,'' Mr. Lautenberg, former chairman of Automatic Data Processing, told the Senate. Mr. Lautenberg said schools in poor districts were averaging 25 percent fewer computers than other schools. Almost 70 percent of schools in wealthy districts have micro-computers; almost 60 percent of poor schools do not, he said.

''In an age that demands computer literacy, a school without a computer is like a school without a library.'' -Senator Frank R. Lautenberg, Democrat of New Jersey. (B1:6.)

Some House Democrats expressed uneasiness today that the proposal by Speaker Thomas P. O'Neill Jr. to limit the benefits of the July 1 tax cut could backfire politically. Mr. O'Neill proposed Monday that when the reduction in tax rates took effect, the maximum benefit to any one taxpayer be limited to $700; this would affect those earning more than $50,000 a year. At a party caucus, the Democrats generally supported the plan. But they also voiced strong apprehension that President Reagan could turn the issue against them in next year's elections.