What was going on when I was born?

A 23-year-old Harvard graduate who came to New York City this fall to study acting was forced at knifepoint to the roof of her Upper West Side apartment building early yesterday and stabbed to death when she resisted being raped, the police said. The victim, Caroline Isenberg, died on an operating table at St. Luke's Hospital at 7:30 A.M., six hours after being stabbed repeatedly in the chest on the darkened roof of her seven-story building at 929 West End Avenue, between 105th and 106th Streets. Before she died, Miss Isenberg, who was said to be lucid and eager to talk despite her wounds, provided the police with an account of the assault. The killer escaped over the roof of an adjacent building as police officers summoned by neighbors raced to the scene. ''There was a hell of a struggle up there,'' said Noreen Williams, a sixth- floor resident, who heard the victim's screams from the roof at 1:30 A.M. and called the police. ''I heard the whole thing, but there was nothing I could do about it. There was nothing anybody could do about it.

Although the profound changes in tax policy proposed by the Treasury last week would eliminate major breaks for business, no single wave of opposition has yet to emerge from the corporate world. In fact, some corporations, at least in public, are putting in a good word for the principle of tax simplification and a more equitable system even as they complain about provisions that would hurt their industry. Not all industries would suffer equally under the changes. Basic industries might find capital formation more difficult, business people say, but service industries might benefit. Specifically, the Treasury's proposal would eliminate the investment tax credit, curb accelerated depreciation schedules and end much of the preferential treatment of capital gains. Some executives see these and other provisions as disruptive to the economy. But the plan would also lower the basic corporate tax rate to 33 percent, from 46 percent, a change that elicited some support.

For the second time in two years, Davvid H. Hoag, the new chief executive of the LTV Steel Company, has unexpectedly moved up to the No. 1 spot at a company. And for the second time in a row, the 45-year-old Pittsburgh native takes the helm when his company is mired in hard times. In April 1983, Thomas C. Graham suddenly resigned as chief executive or the Jones & Laughlin Steel Corporation, a subsidiary of the Dallas-based LTV Corporation, nd Mr. Hoag was called on to fill the top spot. That move came at what was probably the steel industry's bleakest time since the Depression. And l ast Thursday, E. Bradley Jones, chairman and chief executive last June 28 when Jones & Laughlin merged with the Republic Steel Corporation - resigned unexpectedly, and Mr. Hoag has again taken the helm. This time, he takes over not only when much of the arduous job of merging the two steel behemoths remains undone but also when the industry is staggering from a plunge in demand and prices.

The Senate's new Republican leaders gave their first estimates today of how much they think President Reagan should slow the growth of military spending to help reduce Federal budget deficits. The leaders insisted that cuts in growth would have to be made, despite the White House contention that such restraint might compromise arms control talks with the Soviet Union set to start in January. First Indication of Magnitude Republican Congressional leaders have previously told the President that the military budget should be included in any package of spending reductions he proposes to Congress, but the comments made today were the first indication of the amount of restraint the leaders want to see in the military budget. Bob Dole of Kansas, the new Senate majority leader, suggested reductions in projected military budgets totaling $30 billion to $50 billion over the next three years. He said reductions of that magnitude should be part of an overall $200 billion deficit reduction package designed to bring the deficit well under $100 billion by the fiscal year 1988. The deficit is projected at about $210 billion this year.

The day of John Michael Paddack's first celebration of mass was a gift of cold winter sunshine. The Lord, said Father Paddack, had blessed this day with His strong hand and with His gentle hand - the bite of winter and the warmth of the sun. ''I looked in the mirror this morning and I didn't see any physical change, but I felt a confidence and a sense of happiness that I had never felt before,'' said Father Paddack, one of 17 priests who had been ordained Saturday at St. Patrick's Cathedral in Manhattan. ''I knew that God had affirmed my decision.'' The group, from St. Joseph's Seminary at Dunwoodie in Yonkers, was the largest to enter the priesthood in New York since 1971. Saturday had been a glorious ceremony for them, an emotional linking of 17 men to generations of priests who had served the church. John Paddack had walked beneath the vaulted arches of the cathedral, laid his body on the altar and committed his life to God.

A review of the New York City Ballet on Saturday missidentified the leading dancer in the scond section of ''Western Symphony.'' He was David McNaughton.

Despite languid production and declines in the index of leading economic indicators, few economists are expecting a recession soon. Pessimists, who believe that the sharp slowdown in economic growth this fall meant that the nation was headed for another recession, had their position bolstered by Thursday's announcement that the index of leading indicators declined in October. This index, intended to forecast the course of the nation's economy, has slid 2.8 percent since it peaked in May. Such a dip often portends a recession.

Organizations that depend on charitable contributions would be severely hurt if the Treasury Department's plan for revising the income tax system were adopted, according to spokesmen for religious groups, universities, foundations, cultural institutions and associations providing services to the needy. They said contributions from individuals, which totaled $53.8 billion last year, could be cut as much as 20 percent. ''The Treasury proposals would have absolutely devastating impact on the very nonprofit organizations that President Reagan is asking to carry a larger responsibility for services to people,'' asserted Brian O'Connell, president of the Independent Sector. ''I'm speaking about homes for the aged, day-care centers, international relief organizations, environmental and advocacy groups, colleges, symphonic orchestras and the list goes on and on.''

Leading international banks and the United States Government agreed last night to provide Argentina with more than $18 billion in credits to help the Latin American country restructure its foreign debts. The agreement with Argentina, the third-biggest debtor nation among the developing countries, after Brazil and Mexico, was seen as a major step in stabilizing the world financial structure and in strengthening the financial underpinnings of some of the biggest banks in the United States. Under the agreement, Argentina's creditor banks would lend it $4.2 billion in new loans and the United States Government would provide a short-term credit of $500 million. The banks also would lengthen the terms and reduce the interest rates they charge on $13.4 billion of outstanding loans currently due in 1984 and 1985.

EAST RUTHERFORD, N.J. If the Giants had a 5-9 record, Coach Bill Parcells would be getting the blame, if not the gate. Instead, the Giants are 9-5, two victories away from finishing in first place for the first time since 1963, and Bill Parcells deserves much of the credit. In only his second season as head coach, he has molded the Giants into what they haven't been for two decades - not merely a playoff contender, as they were in 1981, but a championship contender. Bill Parcells is a quiet, pleasant man without an obvious ego. After the 20-10 victory over the Jets in Giants Stadium yesterday, he talked at his news conference in the cliches coaches use.

Since the terrorist attack on the American Embassy in Lebanon in September, the State Department and its diplomats abroad have gone on what amounts to a war footing. This has transformed not only the physical appearance of the department and its missions abroad but the psychological outlook of those serving there as well. ''It's sad to see the bunker mentality,'' a longtime State Department official said the other day. ''But how can you complain when we're so naked everywhere?''

In a cloistered gray brick building here that resembles a fraternity house for entrepreneurs, the Rensselaer Polytechnic Institute is helping new companies go into business. Its example is being copied nationwide. R.P.I.'s project, which it calls an industrial incubator, gives newly formed high-technology companies work space at low rent, business services at low cost and opportunities for consultation with its science faculty. The aim is to help the entrepreneurial tenants survive their first 12 to 24 months, a perilous time for most new business ventures. Activity Around New York Since R.P.I. opened its incubator four years ago, similar projects have been started across the country by other universities, quasi-governmental agencies, private corporations and cities.