What was going on when I was born?

WEST HARTFORD, Conn. Around 8 o'clock each weekday morning a handful of cars pull up in front of the neatly kept frame home here belonging to Susan and Paul DeLude. Toddlers and infants ranging from a few months to 4 years old are escorted inside. The children, who never number more than six, scamper into the den adjoining the gleaming white kitchen or run down to the blue and white playroom the DeLudes have built for them in the basement. If the weather is fine, they will go outdoors to play in the small backyard. Mrs. DeLude, trim, dark-haired and 38 years old, is one of a growing number of licensed home-based day-care operators who take care other people's children for a fee. Yet while she has won the admiration of the mothers whose infants she has helped raise over the last nine years, Mrs. DeLude, and others like her, are not necessarily highly regarded by their neighbors. Instead, hundreds of these home-based day-care facilities are the focus of a controversy that is dividing communities all over the country, according to officials at the National Advocacy Project on Family Day Care at the Children's Foundation, a nonprofit organization in Washington, financed in part by the Carnegie Foundation.

A change in Mexico's policy in Central America is sensed by Reagan Administration officials. They said they believed that Mexico was retreating from its strong support of the Sandinista Government in Nicaragua and the leftist insurgents in El Salvador. (Page A1, Columns 4-6.) The trial of four Solidarity advisers on charges of plotting to overthrow the Polish system was adjourned by a military court in Warsaw. The tribunal cited a pending decision in Parliament this weekend on a general amnesty for political prisoners. The defendants are Jacek Kuron, Adam Michnik, Zbigniew Romaszewski and Henryk Wujec. (A4:3.)

A report in the Executive Changes column of Business Day yesterday incorrectly described an appointment by Exovir Inc. Richard D. Glaser was named president and chief operating officer.

Walter F. Mondale won the 1984 Presidential nomination of the Democratic Party tonight, capping a grinding campaign that tested his stamina and exposed deep divisions within the ranks of his party. Delegates to the 39th Democratic National Convention nominated the former Vice President on the first ballot.

Bolstered by a surge in apartment and condominium construction, new housing was started at an annual rate of 1.9 million units in June, up from a 1.8 million rate in May, the Government reported today. The 5.3 percent rise in housing starts over all came despite a 7.2 percent drop in starts of new single-family homes to their lowest levels since December. The Commerce Department report confirmed predictions by private analysts that rising mortgage rates have dampened construction activity by making houses too expensive for many prospective buyers. It also indicated that high mortgage rates had driven many potential single-family home buyers into the rental market.

ROBERT J. COLE Rupert Murdoch, the Australian- born publisher, told directors of the St. Regis Corporation yesterday that he was prepared to pay $52 a share - or $757 million in cash - for enough stock in the company to give him 50.1 percent control. He asked for a response from St. Regis by Monday. Mr. Murdoch said he had received ''assurances'' that a banking syndicate headed by the Midland Bank of London would provide ''not less than'' $750 million in financing. The balance of the cash needed to gain control, he said, would come from funds on hand and existing credit facilities.

Kathleen Larkin, an actress and producer of television commercials, moved back to New York recently after six years in Los Angeles and began to look for an apartment in Manhattan. ''I saw an ad for a loft on Broadway and 18th Street renting for $1,000 a month,'' she said. ''I called and asked why it was so low, and they said, 'What's the matter, don't you trust us?' '' She went to the apartment and found that the bathroom had no shower and no bathtub. There was no heat, no kitchen and no pipes for a kitchen. ''You supply your own,'' Miss Larkin was told, ''and we'll knock $50 off the price.''

The American Telephone and Telegraph Company, which disappointed investors with first-quarter earnings of 20 cents a share, reported yesterday that it earned 43 cents a share in the second quarter, well above analysts' expectations. The company said its net income in the latest period was $455 million on revenues of $8.63 billion. Figures of a year earlier are not comparable because of the Jan. 1 breakup of the Bell System. In this year's first quarter, A.T.&T. earned $227 million on sales of $8.14 billion.

The New York Stock Exchange and the American Stock Exchange announced yesterday that they are thinking of instituting round-the- clock trading to reflect the increasing internationalization of the financial markets. A first step that could begin within the next few months may be the extension of trading hours by one or two hours beyond the current 10 A.M.-to-4 P.M. period, traders on the floors of the exchanges speculate. Trading hours on the Amex and the Big Board have been from 10 A.M. until 4 P.M. since 1974. Before then, exchanges closed at 3:30 P.M., except for a period in the late 1960's, when because of a back office paperwork crunch, it closed at 3 P.M. and was only open for trading four days during the week. But there is some precedent for longer hours. Years ago, trading extended into Saturday mornings.

The St. Regis Corporation, the nation's largest newsprint producer and a major forest products company, is now facing the third takeover attempt in six months, and some analysts say stockholders will not allow the company to pay ''greenmail'' to escape, as it has done twice before. The alternative to greenmail - the costly buying back of stock held by an unfriendly suitor - is likely to be either a sale to the publisher Rupert Murdoch, who approached St. Regis with a takeover offer yesterday, or to a friendly suitor, analysts say. To the St. Regis management, both choices represent defeat of a business strategy that in recent months seemed to be shaking St. Regis from the doldrums. Slow-Moving Company In a effort to cope with its problems of cyclical operations and some low- margin businesses, St. Regis has moved slowly in the eyes of market analysts. This, in turn, has invited the acquisitive eye of such as Mr. Murdoch, Sir James Goldsmith, the British investor, and the Loews Corporation. St. Regis bought out the shares of both the British financier and Loews, but now faces Mr. Murdoch.

Connecticut is short 13 lifeguards at its state- run beaches and parks. The food stands at Jones Beach State Park on Long Island are shy 30 cashiers and dishwashers. And in Morris County in New Jersey, officials need 19 teen-agers for crews to clear brush, paint bridge railings and work as flag bearers on highway-repair gangs. For the first time in years, experts say, the economy in the suburbs around New York City is steaming along so well and spinning off so many jobs that some employers accustomed to an overflow of summer job-seekers cannot find enough workers. Analysts of the labor market and business executives say the shortages have popped up in suburban restaurants and malls, fast-food chains, novelty shops, small retail stores and in traditional outdoor summer work that usually attracts droves of teen-agers and college students.

Construction of new homes rose to a 1.9 million-unit annual rate in June, from 1.8 million in May, bolstered by a surge in apartment and condominium building. At the same time, starts of single- family homes fell to their lowest point since December. Economists noted that high mortgage rates are driving prospective home buyers to the rental market. (Page D1.) President Reagan signed the Deficit Reduction Act, raising taxes $50 billion and cutting spending $13 billion through 1987. (D13.)