What was going on when I was born?

One of the oldest financial services companies for the garment trade, the William Iselin Company, yesterday said that it had sued its former chief executive and two former employees, charging them with conspiring with a large apparel group to defraud Iselin of more than $15 million from 1978 through 1982. The company, a subsidiary of the RCA Corporation's C.I.T. unit, filed suit in the United States District Court for the Southern District of New York against five individuals and several businesses. It charged them, along with 10 unnamed individuals, with a pattern of fraudulent activity that it said violated a number of Federal statutes. The charges involve what Iselin said was a tangle of invoices on sales that were never made, backed up by false bills of lading and forged signatures. The proceeds of the fraud, the complaint says, went to buy real estate, race horses and an interest in a professional basketball team, as well as the establishment of businesses in the United States and abroad.

An obelisk-shaped apartment tower would rise more than 425 feet on West 70th Street if the Landmarks Preservation Commission approves a plan offered yesterday in a stormy meeting. Because the needle-like building, which would be one of the tallest on Central Park West, would extend over the landmark Congregation Shearith Israel Synagogue, the commission has the last word on the matter. That word will not come until Sept. 27 at the earliest. The developers said they would need no further city approval, as their building follows existing zoning rules.

With attitudes ranging from ''New York Is So Exciting'' and ''All the Critics Love U in New York'' to ''I'm Never Going Back to New York City,'' songwriters have been producing a bumper crop of songs about New York. For one reason or another, lyricists and composers seem to be finding the city more inspiring these days. ''It's a new golden age for songs about New York,'' said Hal David, the songwriter who is president of the American Society of Composers, Authors and Publishers, or Ascap. Such is the magic of the city's name, for songwriters at least, that their offerings of recent years have included ''N.Y.C.,'' ''Native New Yorker,'' ''I Love New York,'' ''New York State of Mind'' and at least two songs called ''New York, New York,'' one this year and one in 1977. More than 500,000 copies have been sold of ''Night and Day,'' a 1982 long-playing record album containing ''Chinatown'' and other rock songs about the city by Joe Jackson. ''I Love the New York Yankees,'' written in 1981 by Paula Lindstrom, has become the team's theme song.

One of five fugitive Solidarity leaders has turned himself in and called for an end to the clandestine struggle, the Polish state television reported tonight. Wladyslaw Hardek, leader of the Nowa Huta steel mill, a Solidarity stronghold, was shown on the evening newscast reading a statement saying he regretted causing divisions among Poles. The newscast said he surrendered Monday. He is the highest-ranking resistance figure to have responded to a Government campaign to persuade opposition figures to give up. Mr. Hardek, one of the chief organizers of the resistance, had been in hiding since martial law was imposed on Dec. 13, 1981.

President Reagan criticized the ''so-called peace movement'' today, saying its supporters ''would wage peace by weakening the free.'' In a speech to a veterans' organization here, Mr. Reagan also claimed slow but steady progress for his foreign policy as well as for his arms control and rearmament programs. ''Peace is a beautiful word, but it is also freely used, sometimes even abused,'' the President told a national convention of the American Legion. Those who abuse it, Mr. Reagan said, are engaged in a campaign of ''modern hype and theatrics.''

The Bancal Tri-State Corporation, rejecting an 11th-hour, $298.9 million bid from Wells Fargo & Company, said today that its directors would not reverse the decision to accept a $282 million takeover bid from Japan's Mitsubishi Bank Ltd. The agreement drew immediate criticism from some bank securities analysts who felt the lower bid was not in the shareholders' best interests. And Carl E. Reichardt, Wells Fargo's chairman and chief executive officer, termed the agreement ''shocking.'' He did not say whether Wells, the nation's 13th-largest bank holding company, would take its offer directly to Bancal holders by mounting an unfriendly takeover battle.

The Economy Consumer prices rose 0.4 percent in July, the Labor Department reported, and economists predicted that inflation will continue at almost 5 percent a year. Food prices actually declined, with consumers paying less for some cuts of beef and pork and some fruits and vegetables than they did a year ago. But all other major categories of the Consumer Price Index posted small increases. (Page A1.) In the New York City area, prices rose 0.2 percent. (D3.) Hundreds of corporations are drawing up computer disaster survival plans, and many companies are offering backup services. To show the potential impact of a computer failure, a study found that banks would survive one by just two days, distributors by 3.3 days, manufacturers by 4.8 days and insurers by 5.6 days. (A1.)

Three years ago, officers of the Continental Illinois Bank, this city's largest, were laughing all the way to their vaults over the management comedy at its archrival, the First National Bank of Chicago. First Chicago was losing a host of venerable clients to Continental, including Inland Steel, the Pritzker family and Field Enterprises. There had been embarrassing disclosures of loans to Burt Lance and to the Hunt family to finance its ill-fated silver capers. Profits had been sliding for five straight quarters and First Chicago's top executives seemingly spent as much time fighting among themselves as they did chasing new business. Now, the roles are reversed. Continental, still licking its wounds from the failure of the Penn Square Bank, which cost it millions of dollars, is humble and retrenching, while First Chicago is rolling ahead.

The Federal Aviation Administration allows airline pilots to fly their first commercial flights on a Boeing 767 without ever having taken the plane off the ground. Instead, the pilots log hundreds of hours in earthbound machines that duplicate flight so realistically, airline officials say, that the machines can be better for training than the real thing. Pilots can be put through a variety of emergencies - such as responding to cabin fires, defective engines or icy runways - that would be highly inadvisable with actual aircraft. Link Controls 40% of Market The 767 simulator is one of a long line of such devices built by the Link flight simulation division of the Singer Company. Link, based in Binghamton, N.Y., is said to control about 40 percent of the market for custom-tailored military and commercial flight trainers. Estimates are inexact, but two years ago, Frost & Sullivan, a market research firm, said the market was worth about $1.25 billion a year.

ONE of the time-honored rules of menu planning is that you should avoid duplicating a particular flavor, texture or ingredient during a given meal. If you serve pasta with tomato sauce, for example, you should not use tomatoes in any other form during the meal, be it in appetizer, soup, salad or main course. Brooke Swenson is an inventive cook with a lively sense of humor who not only has defied that basic tenet but has done so with highly satisfactory results. Not long ago, I heard, she served a meal at her home in Weston, Conn., each course of which consisted of one primary ingredient: zucchini. The interesting thing was that the guests were unaware that every dish they ate was based on it. Only in the salad - made with thin, cold, briefly cooked slices - and in the rice, cooked with grated zucchini, did they detect its presence. A midsummer challenge provoked Mrs. Swenson to carry out this amusing feat, she explained when I called. ''At harvest time I become, like many country wives, the victim of my husband's garden, the bumper crop of which issues from the corner devoted to that green Italian squash.

THE wind whipped up sheets of rain as the Northern Star II made its way somewhat unsteadily from the small coastal village of Stonington en route south to the Camp Island mussel- lease farm. As Bobby Burgess wrestled the 40-foot fishing boat through a series of choppy channels among the tiny, fir-covered rocky islands of Jericho Bay he wondered about the weather and the beginning of the mussel season. ''Wouldn't be out here this morning,'' he said, wiping the water from his eyes and keeping the Northern Star II on course, ''except that Frank called and said he was starting up.'' Mr. Burgess was referring to Frank Simon, vice president and co- owner of Great Eastern Mussel Farms, and the urgency indicated by ''starting up'' meant that the early-summer hiatus in the Maine mussel-farming season was over and the concern was ready once again to receive, process and ship the mussels that Mr. Burgess and his partner, Jack Hamblen, would bring in.

The chief Philippine opposition leader asked today in Parliament how an assassin had been able to approach Benigno S. Aquino Jr. on a heavily guarded airport runway, and why the Government had issued practically no information on Sunday's killing. ''How was it that he was allowed to approach the plane?'' Salvador H. Laurel asked about the man the Government says killed Mr. Aquino, the country's best-known political rival of President Ferdinand E. Marcos. ''How was it that the assassin knew exactly where to wait for Senator Aquino?'' Suspect Still Not Identified Mr. Aquino was shot dead as he walked away from a jetliner that had carried him home after more than three years in the United States. The man the Government says was the slayer was shot dead by security guards. He has not yet been identified.