What was going on when I was born?

The Justice Department's antitrust division today asked the nation's largest telephone companies to provide information on the agreement they reached to provide a new type of mobile phone service in 30 of the nation's largest cities. The antitrust division served information requests on the American Telephone and Telegraph Company, the General Telephone and Electronics Corporation, United Telephone System Inc., the Continental Telephone Corporation and several other companies as part of what it described as a preliminary inquiry. Tom Stewart, a spokesman for the Justice Department, confirmed that a preliminary inquiry had been started. But he declined to confirm or deny that the companies had actually been served with civil investigative demands, as the preliminary requests for information are known.

HATTIE CARTHAN adopts things. When she lived on Long Island as a young girl and drove to and from Brooklyn church services with her father, a minister, she used to ''adopt trees along the road because they came to be familiar to me,'' she says. ''They were my trees.'' She never lost her fondness for trees, and 13 years ago, when she found a rare magnolia tree abloom in front of one of four decaying brownstones on Lafayette Avenue a few blocks from her home in the Bedford-Stuyvesant section of Brooklyn, she adopted that, too. The fact that the tree was very much a botanical freak, reckoned to be almost 100 years old and a species rarely able to tolerate climate conditions north of Baltimore, made it all the more dear to Mrs. Carthan, somewhat akin to an orphan in need of special care.

At lunchtime these days, on the great stone steps of the New York Public Library at 41st Street, they are celebrating the joy of summer. Lunchers lunch, hawkers hawk, gawkers gawk, fiddlers fiddle, preachers preach and thousands of passers-by stop, stare, smile and then move on. That much is not new. What is new is the rejoicing inside the Beaux-Arts building, where library officials are celebrating the end of the first really good year in a long, long time.

Several months ago Dartmouth College called the architectural firm Moore Grover Harper in Essex, Conn., asking for design revisions in an art gallery still in the planning stage. Normally an architect and one or more draftsmen would spend about three days modifying the design, changing the specifications and redrawing the building. This time an architect made the changes on a video screen in a matter of hours and new drawings were in the mail the same day. Such a quick turnaround, which was impossible last year at this firm of 21 employees, is routine now with the help of a computeraided design system (CAD), the latest advance in the computer revolution. ''In the old days an architect did most drawings on scratch paper and then gave them to an employee who made the formal pencil drawings with triangles, compasses and all that,'' said William H. Grover, a partner in the firm.

President Reagan's offer of American troops to help guarantee the evacuation of Palestine Liberation Organization forces from west Beirut seems to mark a new turn in what has amounted to an awkward diplomatic minuet between the United States and the Palestinian organization for the last seven years. During this period, the United States has followed a policy of refusing to deal with the P.L.O. until it met certain Israeli conditions. In the indirect negotiations that Philip C. Habib, the special American envoy, has conducted in Beirut with the Palestinians, there is still no sign that the policy is about to change. But some officials said that once the Lebanese crisis was over, and if the Palestinian leadership emerged intact, more productive discussions might develop. Administration officials said today that the move to extricate the Palestinians from possible annihilation by Israel came after their leaders had urged the United States repeatedly to drop its ban on direct diplomatic contacts.

The International Telephone and Telegraph Corporation said yesterday that it had reached a preliminary agreement to sell its largest French subsidiaries, Compagnie Generale de Constructions Telephoniques and Laboratoire Central de Telecommunications, to the French Government for $50 million. The agreement followed months of negotiations with the Socialist Government of President Francois Mitterrand, who instituted a program to nationalize a number of major companies and banks after he was elected in May 1981. The French I.T.T. subsidiaries, consisting of a manufacturer of telecommunications equipment and its electronics laboratory, account for more than half the revenues I.T.T. derives from France, the company said. Both generated small profits last year, but lost money in each of the preceding three years, said James Gallagher, an I.T.T. spokesman in New York. He declined to specify the extent of the French subsidiaries' losses or revenues.

An effort to stem the sweep of rabies across Europe by sprinkling the landscape with chicken heads containing live rabies vaccine has proved so successful in a limited area of Switzerland that the same strategy will be used throughout the Alps between Zurich and Geneva this summer. The program initially aroused fears that the live virus itself might become virulent and help the disease spread, but there is no evidence that it has. The chicken heads are distributed along roads and trails, as well as by helicopter in remote areas, as bait for foxes, who are the chief carriers of the disease in Europe. After eating the bait the foxes become immune to rabies, breaking the transmission cycle of the disease, which has seriously afflicted at least a half dozen European nations and invaded several others.

Antitrust officials asked the largest telephone companies for data on their plans to form joint ventures in a new type of mobile phone service called cellular radio, a computer-based technology that is expected to revolutionize the industry. Although the full import of the request was not immediately clear, one official confirmed that a preliminary inquiry was underway. (Page D1.) The F.T.C. dismissed charges that The Los Angeles Times had unfairly favored large advertisers by charging them substantially lower rates than lower-volume or one-time advertisers. The agency also ruled that Russell Stover Candies illegally coerced retailers into selling chocolates at ''suggested'' prices. And it upheld the right of Beltone Electronics to require dealers to sell its hearing aids only within assigned areas and to deal exclusively in its products. (D5.)

The dead-eyed, somber faces appear on the television screens and a cold voice says, ''Commit a crime with a gun in Pennsylvania and this is what you're in for.'' Then comes the jarring sound of a steel-barred door clanging shut. ''For five years,'' the voice hisses. The commercials herald the start of Pennsylvania's mandatory minimum sentencing law for violent criminals, just one of numerous proposals to curb violent crime in the state. The others encompass nearly every corrections and crime-fighting concept offered nationwide. Mandatory minimum sentences have been enacted in other states. So has the abolition of parole boards. So has the accumulation of ''good time'' as a disciplinary tool for prison inmates. So have lengthened sentences for certain crimes, and strengthened corrections departments, and large-scale construction of new cells.

The Diamond Shamrock Corporation, a Dallas-based energy and chemicals company, said yesterday that it had signed a letter of intent to acquire the Sigmor Corporation, one of the largest independent gasoline retailers in the United States, in a stock and cash deal valued at $160 million. Despite Wall Street speculation that the deal was crafted to increase Diamond Shamrock's outstanding shares as a tactic against an unfriendly takeover, the company insisted that its principal motive in acquiring the closely held Sigmor was a desire to increase operating profits. As such, Diamond Shamrock appears to be going against a tide of poor results on the part of its refining and marketing operations over the past year. ''It's a lot cheaper to buy something when it's unpopular,'' Charles O. Yoakum, Diamond Shamrock's manager of media relations, said.

Despite public reservations by Yasir Arafat, chairman of the Palestine Liberation Organization, the United States moved ahead today with plans for the possible use of American troops to assist the evacuation of Palestinian guerrillas from west Beirut and for insuring the safety of the American units. Administration officials said the United States had been advised privately through diplomatic channels not to take seriously the cold public reaction of Palestinian leaders to the still tentative evacuation proposal. The White House has received word, these sources said, that P.L.O. leaders want the United States to proceed. In California, where President Reagan was kept abreast of the diplomatic and military developments by William P. Clark, his national security adviser, Larry Speakes, the White House spokesman, said the negotiations had reached ''a sensitive stage'' and voiced some optimism about prospects for Palestinian agreement to the plan involving American troops.

''For some reason, a glaze passes over peoples' faces when you say Canada.