What was going on when I was born?

Despite President Ferdinand Marcos's most vigorous efforts to dispel it, the ghost of Benigno S. Aquino Jr. continues to haunt the Philippines. Last week, the high-level commission the President had appointed to investigate the murder of Mr. Aquino, the opposition leader, abruptly quit, in response to widespread doubts about its impartiality. The commission had been stymied by lawsuits and skepticism that Marcos appointees would find the culprit. The first chairman, Chief Justice Enrique Fernando, took the criticism seriously and quit. The President's next choice as chairman, Arturo Tolentino, a Foreign Ministry official, rejected the job as ''cosmetic.'' Five other commission members - four retired Supreme Court justices and a member of Parliament - also quit.

WASHINGTON PRESIDENT REAGAN'S abrupt decision to nominate William P. Clark, the national security adviser, to be Secretary of the Interior had immediate implications for foreign and domestic policy, campaign politics and the Reagan Presidency. It also offered a window on the relationship of two close friends and on a paradox of the President's style. Reliant as he is on his aides for guidance, Mr. Reagan's independence of mind can still startle. Mr. Clark was not on any original staff list of candidates to succeed Interior Secretary James G. Watt, who resigned a week ago after Senate passage of a measure calling for his ouster became a certainty. Neither James A. Baker 3d nor Michael K. Deaver, the White House chief and deputy chief of staff, was reported to be happy with the Clark choice. Though both had had sharp differences with Mr. Clark in the White House, both also wanted to fill the Interior post with a political figure who could reassure Mr. Reagan's western political base and defuse the hostilities of environmental groups. Mr. Baker and Mr. Deaver saw a happy coincidence in the fact that such an opportunity came just as the President gave formal approval to the formation of a re-election committee. Having passed the week wooing a series of prominent western Republicans, they are now bracing for a confirmation fight that is sure to revive the antagonisms they had hoped would fade with Mr. Watt's departure.

DASHIELL HAMMETT A Life. By Diane Johnson. Illustrated. 344 pp. New York: Random House. $17.95. If you were to go merely by the quantity (rather than the quality) of his imitators, you could argue that Dashiell Hammett was a more important writer than James Joyce. There were one or two writers of at least parboiled crime fiction before Hammett, but Hammett gave his imitators more than an attitude. He gave them a cast of characters, a resilient plot, a setting, a repertory of images, a style, a keyhole view of society, an ethos and, above all, a hero. Sam Spade is an old American type brought up to date, Hawkeye become private eye with fedora and street smarts instead of leatherstockings and wood lore, his turf the last frontier of San Francisco. The invention of a new popular genre is to the lesser world of literature what the invention of a new form of government is to the larger world of institutions - and just as rare. There are good reasons, then, for reading or writing a biography of Hammett, and Diane Johnson's cool, steady-eyed and engrossing ''Dashiell Hammett'' is the third in as many years.

-cut insurance needs of rental tenants, who should cover their furnishings and personal belongings, or the owners of a house, who should cover the structure as well as its contents, the coverage requirements of a condominium or cooperative owner are complex. If the buyer of a condominium or cooperative is financing with a mortgage, the lender will want proof that the building's structure is covered. This coverage is taken out by the governing board of the building, and further coverage is discretionary. ''What the person wants to do about his own unit is up to him,'' said Arthur Carter, assistant mortgage officer at the Dime Savings Bank of New York.

When 32-year-old Mitchell L. Kapor took his fledgling computer software company, the Lotus Development Corporation, public less than two weeks ago, he made a fortune - roughly $70 million in fact. That this former radio disc jockey and teacher of transcendental meditation turned to computer programming only a few years ago simply adds to the feat. It is the stuff of which legends are made, especially in the personal computer software business. Throughout the land, other young and ambitious entrepreneurs are toiling away late into the night struggling to write that next great piece of software - a set of instructions, usually embedded in a gray disk, that allows the nation's computers to perform useful tasks. These lone programmers working in their basements are also dreaming of creating the next Lotus. But such visions may be unrealistic - for Mr. Kapor's accomplishment, dramatic as it may be, is no rags-to- riches success story. Mr. Kapor was amply backed by nearly $5 million in venture capital. To introduce its personal computer program, called simply ''1-2-3,'' Lotus spent more than $1 million in advertising in a three- month period - an unprecedented level for the industry.

On Saturday - 100 years to the day it opened its doors in 1883 - the Metropolitan Opera will celebrate by running an all-day marathon. Promised are some 70 singers who will flock on and off the stage at the matinee and evening events. It will be a circus. If past such events are any indication - at the festivities connected with the closing of the old house in 1966, for instance - every opera buff will be clamoring for tickets. Fan clubs will be out in force to cheer on their heroes and heroines. Tears will be shed as a few old-timers lift their voices, in solo or in combination. Not that there will be many old- timers on stage, as there were in 1966. The preponderance on Saturday will be singers currently in action at the house. Some of those are internationally famous, some are at the outset of what may or may not develop into a fine career, some are comprimario singers who specialize in secondary roles, some are not really very good. How many of the 70 - 70 count 'em 70 - would have been allowed on the sacred stage of the Metropolitan Opera at the turn of the century? But, then again, how many supersingers are currently before the public? Everybody says we are in a weak age of singing, notably deficient in the big voices needed for the Wagnerian and heavier Verdi roles. And it is true.

James Galloway was smiling as he watched a giant green combine rumble past drying stalks and spout its yellow burden of harvested corn into waiting trucks. But it was impossible to tell at a glance whether he was pleased. In this season of drought and dashed hopes, many farmers wear twisted grins that disguise their dismay over mounting losses. But with his first words came evidence that the slender, 37-year-old Mr. Galloway, like his neighbors Phil Overman and Kenneth Bodenhorn, was among a limited number of growers scattered through the drought areas who are doing relatively well. National Projections Raised ''That corn,'' he said, looking at the field beyond the combine, ''is running at 130 to 140 bushels an acre.''

With precision and pinch-hitters, the Baltimore Orioles moved to one game of winning the 80th World Series today when they defeated the Philadelphia Phillies for the third straight time, 5-4. The American League champions extended their lead to three games to one before 66,947 fans in Veterans Stadium, the largest Series crowd in 19 years. And they were not deterred by the return of Pete Rose after his one- night exile as a nonstarter. The Orioles will try to finish the job Sunday, with Scott McGregor pitching against the rookie Charles Hudson, who lasted less than five innings last Wednesday, when the Baltimore streak began. ''After you lose the first game,'' said Joe Altobelli, the Oriole manager, ''it's not easy to come back and win three in a row, especially against the Phillies. It brings me one step closer to going home and seeing my grandkids.''

East 70th Street between Fifth and Madison Avenues is an elegant enclave of the arts. At the Fifth Avenue corner stands the Frick Collection.

AS a lawyer based in Newtown and on Long Island, Harvey F. Wachsman practices his trade in an unusual way. If a client happens to mention having lower back pain, for example, the lawyer may take out a stethoscope and proceed to do a full physical examination. Or, while attending a legal seminar in Arizona, he may decide to assist in neurosurgery with a colleague at a local hospital. ''I've always had many interests,'' said the 47-year-old physician-lawyer, who, in 1976 became one of about 600 men and women in the country who have degrees in both medicine and law. Today, more than 800 physicians have gone on to acquire law degrees, and their numbers are growing steadily as more and more medical schools offer courses in legal medicine or combine degree programs.

Room 522: Male, 65 . . . quadruple coronary-bypass surgery . . . very anxious about going home . . . needs to be prepared emotionally . . . wife and daughter still seem confused about his care, although nurses have talked to them many times. Recommendations: Refer for follow-up medical care and restorative cardiac nursing . . . put all instructions for family in writing. * Room 524: Male, 51 . . . diabetic . . . speaks only Spanish. Recommendations: Have bilingual coordinator check to be sure that he knows how to administer his insulin . . . follow up with the patient and his wife. * Room 414, Bed 1: Female, 73 . . . abdominal mass . . . lives with granddaughter. Recommendations: Check on transportation to radiation treatments.

It's been a fixture in a graceful section of Greenwich, Conn., for 115 years, but the stately Victorian house at East Putnam Avenue and Old Church Road is undergoing a transformation. By next February it will have been completely refurbished and turned into the centerpiece of a seven-unit condominium development, Old Church Green.