What was going on when I was born?

Costly and crowded health clubs, modesty and a continuing desire to remain fit have sent thousands of Americans in search of creative and effective ways to work out at home. According to industry estimates, this trend has pushed sales for the home-exercise equipment industry above the $1 billion-a-year mark with no slowdown in sight. Reaping the benefits are companies both large and small that sell - at premium prices - everything from jump ropes and small hand weights to gravity-inversion systems and multi-function gyms that can cost as much as $3,000 or more. ''I've seen a lot of fads in this business, but it's mind-boggling how this home fitness thing has taken off,'' said Robert Carr, editor and co-publisher of Sporting Goods Business, a trade publication. ''The way these things go, it should have died out by now, but there's no sign of easing on the horizon.''

The Islanders were already departed when cars lined the downtown streets in Edmonton, Alberta, and sleepy-eyed children, too young to understand the childlikeness of adults, toddled around in their No. 99 T-shirts. The Oilers won their first Stanley Cup Saturday night, and it wasn't until well into yesterday morning, with the sun ready to rise, that the raised emotions of their fans began to settle down. In New York, with their charter flight touching down well after sunrise, the Islanders drove out along the Grand Central Parkway as losers for the first time in the 1980's. They were home, ready to lounge on Jones Beach or visit friends in Canada, without the Stanley Cup. ''The thought of losing had crossed my mind, especially more vividly in the past few days,'' said Butch Goring as his teammates packed their bags following their season-ending 5-2 loss.

One monitors business credit; the other measures consumer sales. And if neither company is precisely a household word, both the Dun & Bradstreet Corporation and the A. C. Nielsen Company are part of the basic business vocabulary. The merger of the two companies, announced last week, brings together two of the largest and best-established concerns in information services. While there is little overlap between the areas they currently track, the two companies can help each other in a number of ways, according to corporate management and securities analysts. ''We both have the ability to collect a lot of data and deliver it efficiently to clients,'' said Arthur C. Nielsen Jr., who resigned earlier this month as chairman and chief executive after reaching his 65th birthday. He suggested that the new company might delve more deeply into market research for industrial products, as opposed to consumer goods and services.

Arriving in New York City on flights from Geneva or Paris, Albert Camille Gillet gave all the appearances of a prosperous European businessman. A chauffeured limousine usually waited to drive him to Manhattan, where he always stopped at fine hotels and dined at expensive restaurants. In contrast, Jose Martinez-Torres lived in a dingy, poorly furnished apartment in the Bronx, only occasionally traveling out of the city on business trips. The two men are never known to have met. Yet both, according to court records, were recently involved in the same illegal billion-dollar business: trafficking in heroin and cocaine.

The usual crowd was here this weekend. Spinsters Opposed to Nuclear Genocide, Trident Nein, Young Republicans, the Communist Workers Party, the Revolutionary Communist Party, the Libertarian Party, the United Church of Christ, saffron-robed Buddhists, the Ku Klux Klan - 500 protesters and counterprotesters marched and chanted, 300 police officers in riot gear watched over them. ''We've become the focal point for demonstrations - month after month after month,'' said Joseph E. Presslitz, the chairman of the City Council's Finance Committee. ''It begins to wear you down. And now the character of the protests has begun to change. You never know what's going to happen. The cost is enormous.''

MONDAY, MAY 21, 1984 The Economy The historic rescue plan for Continental Illinois brought open- ended assurances from the Federal Reserve and redefined the limits of banking deregulation. After two weeks of turmoil, the crisis was resolved in a hectic 24-hour period. (Page A1.)

Jose Napoleon Duarte, the President-elect of El Salvador, said today that he was confident that the Salvadoran Army would support his efforts to introduce democracy and abolish the right-wing death squads in his country. But in his first public appearance since arriving here Saturday night for a brief visit before his inauguration June 1, Mr. Duarte was also careful to avoid any controversy with the Salvadoran military leadership. He said that after discussions with military leaders he had decided to ask Gen. Carlos Eugenio Vides Casanova to remain as Defense Minister. He said the general, the former commander of the national guard, had accepted his program and had agreed to make ''a declaration of loyalty and support for democracy.''

The British, like many other Europeans, are increasingly frustrated by their poor record at turning technological innovations into profitable, job-creating businesses. ''There is a lot of truth in the criticism that Europe is strong on science and poor at application,'' Dr. Eric Howells, head of research and development at Britain's giant Imperial Chemical Industries P.L.C., said in a recent interview. ''We don't get as good a return on efforts that produce inventions.'' Impact Seen in Many Areas The British and other Europeans describe the impact of their technology problems in many ways. Some cite Europe's lower economic growth rates and the late arrival of the current economic recovery. Others point to Europe's lagging performance in creating new jobs or in private investment in new business ventures. Still others fear that European countries will no longer be able to afford the levels of social spending they have adopted.

Iran was accused of aggression in the Persian Gulf war by the Foreign Ministers of the 21-member Arab League. The ministers accused Iran of aggression against Iraq and specifically in connection with attacks against Arab shipping in the Persian Gulf. In a rare departure from its usual public unanimity, the group overruled objections from Syria and Libya, the only Arab League supporters of Iran. (Page A1, Column 6.) Soviet submarines off the U.S. have been increased by Moscow, and their nuclear missiles are within 10 minutes of American targets, the Soviet Defense Minister, Dmitri F. Ustinov, said. Marshal Ustinov also said the number of SS-20 medium- range missiles in the European part of the Soviet Union would be increased ''accordingly'' if the United States proceeds with its plan to deploy additional Pershing 2 and cruise missiles in Western Europe. (A1:5.)

Because of the Reagan Administration's vast military buildup, the Defense Department has accumulated the largest backlog of unspent funds since the Vietnam War era, creating management and budget problems for the Pentagon and Congress. According to official Government figures for 1981 through 1983, the backlog of money approved by Congress and signed into contracts, yet not paid out by the Pentagon, increased by 89 percent, to more than $128 billion from $68 billion. Over the same period, the backlog of unspent funds awaiting selection of a contractor rose by 79 percent, to $43 billion from $24 billion. Measured in 1984 dollars, total unspent military funding has increased 102 percent since 1974, and 67 percent since 1980. For all other Federal agencies, unspent funding has decreased by 22 percent since 1980.

Despite reports of strong growth during April, many economists believe the economy is slowing and they are sticking to forecasts of 3 to 5 percent growth for the second quarter. From employment to housing starts, and from industrial production to consumer spending, many economic measures soared last month, leading to speculation that the rapid first-quarter gains might spill into the second. But most economists surveyed agreed that the April figures were high because bad weather kept March figures artificially low. Most April figures, they said, were lower than January or February levels, and so would not push the gross national product higher.

The leaders of Reform Judaism called on American blacks and Jews yesterday to preserve their historic social alliance despite ''traumas of the moment'' that they said had been engendered by the Rev. Jesse Jackson's Presidential campaign. The Union of American Hebrew Congregations, which represents 770 Reform synagogues with 1.25 million members in the United States and Canada, urged restoration of the ''coalition of conscience'' that has long made blacks and Jews ''natural allies in the struggle for social justice in America.'' Responding to a growing gulf between the nation's 26 million blacks and 3 million Jews, the union appealed to all Presidential candidates, leaders of public opinion and ''responsible groups in American society to repudiate all threats of violence and appeals to prejudice - indeed, all assaults on the democratic process.'' Deep Distress Noted ''We are deeply distressed by the atmosphere of harassment, threats of violence and appeals to prejudice that have been part of the current election campaign,'' 130 trustees of the union declared in a resolution adopted by a voice vote, with notable dissent, at the end of a three-day meeting in Secaucus, N.J. Some trustees said they opposed reconciliation in the face of what they called black anti-Semitism.