What was going on when I was born?

Prices farmers get for raw products climbed 4.6 percent in August, the sharpest single-month increase in more than three years, the Department of Agriculture said today. Drought throughout the major crop areas and the Government's payment-in-kind acreage program have curtailed harvest prospects sharply this year, helping to drive up market prices of key commodities. Under the payment-in-kind program, the Government repays farmers for idling land with surplus crops.

A thumb-sized plastic knob for the cockpit of the Navy's A-7 jet fighter can cost $400. A tiny machine screw for the Minuteman 2 missile can cost $36.77. A ring seal used in the engine of B-52 bombers can cost $2,020.50. And the Navy paid $435 for an ordinary hammer. Selling spare parts to the military is a $13 billion-a-year business that Pentagon officials and defense-industry executives say is almost impossible to control. Perhaps more than in any other area of military purchasing, spare parts tend to be sold at huge markups under contracts that are signed without competitive bidding by manufacturers who are rewarded even if they deliver their products late. But because the Defense Department buys them in small quantities and because they typically account for only a small fraction of a contractor's total sales, spare parts are rarely subject to close scrutiny. Officials say this means that rapid price increases are rarely challenged.

MORE divorced and separated men are delinquent in making child- support payments than ever before, and it is a phenomenon that social scientists are trying to explain, legislators are trying to remedy and national women's and men's organizations are disagreeing about. Just 46.7 percent of four million American women who were supposed to receive child-support payments are collecting the full amount, the Census Bureau reported recently. The number of delinquents was put at 2.13 million, 380,000 more than when a similar survey was conducted in 1978. ''The reasons these men didn't pay are complex and hard to pin down,'' said Ruth Sanders of the bureau's population division, who compiled the report. ''The reasons may range from not wanting to pay to the possibility that men who see their children less often start paying less. It may reflect the lack of court enforcement or men's financial situation.''

Plans by New York City's private hospitals and medical centers to spend more than $4 billion on renovations and new technology should be drastically cut, the city's federally financed health planning agency advised Governor Cuomo yesterday. The unit, the New York City Health Systems Agency, described the projected costs as ''staggering by any standard'' and ''unaffordable.'' It warned that they would have to be borne by the taxpayers and that they would be damaging for the hospitals themselves, especially those in impoverished neighborhoods. The state regulates all new construction in hospitals, private as well as public, on the ground that public funds, in the form of Federal and private insurance plans, pay for virtually all hospital construction. The New York State Department of Health is now seeking to extend that authority.

The Economy Leading economic indicators rose just 0.3 percent in July, the smallest of 11 consecutive monthly gains, the Commerce Department reported. The figure suggests that the recovery's strong pace, which was worrying many economists, is slowing down. With slower growth, experts said, interest rates might recede a bit. But they cautioned against putting too much importance in a one-month change in the index. (Page A1.) Prices farmers get for raw products climbed 4.6 percent in August, the sharpest such increase in more than three years, the Agriculture Department reported. The increase, after two months of declines, was linked to widespread drought and the payment-in-kind acreage program, both of which are squeezing supplies. (D1.)

''The United States is involved in Lebanon because our effort is indispensable to freedom, peace, justice and stability.

''NO one at my office ever asked me about what it was like to live in the South Street Seaport area before all this publicity about its opening,'' says Stephen Van Anden, a systems engineer with IBM, and a painter. ''Now everybody's curious; one of the executives who's about to retire has even been looking for a place to buy. People are recognizing it's not just a 9-to-5 community.'' Dominick Aiello, a real estate with J. I. Sopher & Company, has also felt an increased interest in living in Lower Manhattan since the opening of the Seaport Museum several weeks ago. ''I'm still in shock over it,'' he said. ''For the last year and a half, I've had 10 to 12 apartment vacancies each month in the downtown rental buildings I handle. Now there's nothing to rent - I've even rented my office.'' The path of Manhattan's residential growth has in the last decade been bearing south, beyond SoHo and into TriBeCa, and is now extending into its logical geographical conclusion, Lower Manhattan. While the census figures of 1970 show a resident downtown population of 500 people, current figures run at about 14,000, according to Paul Goldstein, district manager for Community Board 1.

A Business Day article yesterday incorrectly described discussions between Volkswagenwerk A.G. and the Chrysler Corporation. Exploratory talks about a possible joint venture at New Stanton, Pa., have ceased, Volkswagen says, but discussions of other cooperative efforts continue. A related article appears on page D2.

WHEN the Peruvian novelist Mario Vargas Llosa was a struggling writer in Paris in the 1960's, he and his first wife lived for five years in a one-room walk-up just large enough to hold a bed and a table. But the world has since discovered Latin American writers, and Mr. Vargas Llosa's publishers say that today he is the best-selling of them all. Among his books praised abroad are ''Green House'' and ''Conversations in the Cathedral.'' His latest book to be translated into English, ''Aunt Julia and the Scriptwriter,'' an autobiographical comedy about his poorer days, was published last year by Farrar, Straus & Giroux, is in its fifth printing in hardcover. Now Mr. Vargas Llosa, his second wife and their three children share a striking villa on a cliff here overlooking the Pacific. The house is a blend of modern, Mediterranean and colonial styles dominated by what Mr. Vargas Llosa once lacked most: space and a view.

The Bank of Montreal, which unsuccessfully tried to buy the New York area branches of the Bankers Trust Company in 1978, is negotiating to acquire Harris Bankcorp, the third-largest bank in Chicago and the 36th-largest in the United States, according to banking industry sources. Rumors of such a takeover touched off speculation in Harris stock yesterday, causing the New York Stock Exchange to suspend trading until 11:27 A.M. The stock then opened at 51 a share, up 4 1/4 points from the close of trading on Tuesday. By the end of yesterday's session, it had risen to 57 1/2, up 10 3/4 for the day.

A photo caption accompanying an article on kosher carryouts in yesterday's Living Section incorrectly identified the dish shown. It was a noodle and raisin kugel that contained no cheese or other dairy product.

Lebanon's army counterattacked the leftist Moslem militiamen who had seized large parts of West Beirut. In a major show of force, about 6,000 troops made an armor and infantry assault stretching across all of the largely Moslem half of the capital, and by nightfall the army appeared to have regained control of most key sectors. (Page A1, Column 6.) The Reagan Administration denied for the third day that the American marines in Lebanon had been involved in hostilities or had been the targets of Molsem militia units. Secretary of State George P. Shultz, speaking at a news conference, said there were no plans to increase the size of the contingent or to expand its largely passive mission. (A1:5-6.)