What was going on when I was born?

Down the path into Riverside Park from 90th Street yesterday, the little community flower garden was a surge of color against the iron of the fences and the gray of the river. Bumblebees and butterflies bounced about the exquisitely tended plots, and the burnt orange of the poppies, the mauve of larkspur, the crimson of impatiens seemed to sum up all the natural life long gone under the city's concrete. Joggers and old people stopped to sniff the blossoms, the volunteers who have kept the garden going since spring bent to their weeding and watering. A child with reaching fingers was called back by his father -''!Que no arranque!'' (''Don't pick!'').

President Reagan's decision to propose a one-year extension of the Soviet-American grain agreement has set off a guessing game here about whether the Kremlin will negotiate on Mr. Reagan's terms or let the six-year-old pact lapse. Generally, Western diplomats and businessmen who follow the trade think that the Soviet Union's pressing need for grain imports will impel it to accept a 12-month extension, just as it did when a similar extension was offered last year. This year's Soviet harvest will be a poor and possibly even disastrous one, and Western forecasts are that the Kremlin will be looking abroad again for at least 40 million tons of wheat, corn and other grains. But the Soviet decision is by no means certain. A week after President Reagan announced his decision, choosing a middle course between those in the Administration who wanted a long-term agreement and those who favored abandoning it, the Soviet press has offered no comment on the American move. This in itself suggests that there is debate inside the Kremlin about how to react.

Ray Floyd won the 64th Professional Golfers' Association championship this afternoon, but it was not quite the Sunday stroll he had expected when he started the day with a five-stroke lead. Caught up in daydreaming and making what he called ''bonehead'' mental errors, Floyd played so inelegant a final round that all he could be proud of was the way he ''talked to myself'' to rally between the 12th tee and the 18th fairway. Then he finished with an ignominious double bogey on the 18th hole. In the middle of the round, Floyd was tormented by the thought that he might read he had ''blown'' a five-shot lead in a major championship. ''I could not have lived with it,'' he said.

Rumors of a big strike of uranium ore began spreading through the Catskills early last year, intensifying by spring when land agents at the Sullivan County Courthouse here found that Isadore Gibber had leased the uranium rights on his 164-acre egg farm to a big minerals company. The company later abandoned its hunt for uranium, but the existence of that one lease continues to stir an environmental backlash that has fanned out as far as New York and Philadelphia. Environmental action groups have held rallies to express their alarm. Several thousand people have signed protest petitions. A local resolution has been enacted to ban uranium mining. Fears have been expressed that the watersheds of New York City and Philadelphia might face contamination by radioactive debris.

New York State's Commission of Investigation has identified five areas of possible corruption as its first targets in an investigation of the multibillion-dollar construction industry. The agency will initially focus on allegations of extortion by union officials in return for labor peace, of payoffs to public officials in the awarding of contracts, of rigged bids or antitrust violations by contractors, of organized-crime influence in the industry, and of extortion from contractors by groups claiming to represent nonwhite workers seeking construction jobs, according to Thomas F. Staffa, the commission's chief counsel. Mr. Staffa said the scope of the investigation was based on allegations made to the commission and discussions with state and Federal law-enforcement officials.

In the wake of the Gulf Oil Corporation's abrupt decision to back out of a $5 billion takeover of the Cities Service Company, the chairman of Cities Service said yesterday that his company would go into the market to buy up to 20 million shares of its own stock. The chairman, Charles J. Waidelich, added in an interview that the purchases would start as soon as trading resumed. He said this would give Cities Service, the nation's 16th largest oil company, time to find a new buyer or, failing that, to arrange for the company's ''orderly liquidation.'' He also said that his company's aim was to prevent chaos in the stock market and to protect the stockholders of Cities Service.

Cities Service plans to buy up to 20 million of its own shares in the open market in an effort to prevent their value from declining after Gulf Oil's abrupt decision not to take over the company. Cities Service also is seeking another takeover offer to match that withdrawn by Gulf. (Page A1.) The move by Gulf Oil has Wall Street arbitragers angry and worried: they had bought Cities Service heavily in the hope of cashing in when the $5 billion deal was completed. (D4.)

The economy showed no signs of improvement in July, with new orders remaining weak, employment down and summer production shutdowns being extended, according to a survey by the National Association of Purchasing Management. Although many Government officials interpreted the second-quarter increase in the gross national product as a sign of a turnaround in the economy, the association's report said, ''There is no evidence at all of any pickup in the industrial sector.'' The monthly survey of 250 purchasing managers, who represent 21 industries and 40 states, has been taken since the l930's and includes questions on new orders, production, employment and inventories.

Prime Minister Menachem Begin said tonight that there were grounds to believe that the besieged Palestine Liberation Organization guerrillas ''will leave shortly and that we will not have to enter west Beirut.'' This was his first indication that he seriously considered a peaceful withdrawal of the Palestinian guerrillas from west Beirut to be likely. In a speech at the National Military Academy, Mr. Begin also said he informed Secretary of State George P. Shultz today that Israel had accepted the proposal for a multinational peacekeeping force to enter Beirut, but only ''after most of the terrorists leave Lebanon together with 1,500 Syrians who are besieged there.'' No Timetable Given The Prime Minister, whose speech was given in Hebrew and was shown, in excerpts, on the evening news program on the state-owned television, did not give a timetable for the withdrawal plan. But he did give the conditions under which Israel would agree to the deployment of the peacekeeping force. While he set conditions that might not be desirable to the P.L.O., the Prime Minister made it clear that he expected the guerrillas to leave west Beirut.

''Already today we can look beyond the fighting. It will end, we hope, shortly, and then according to my belief and my knowledge, and my logical presumption, we will have an extended period of peace.''

Forty-eight floors above 42d Street, Lawrence A. Wien sat in his paneled office recently at a large leather-tooled desk, looking out over midtown Manhattan - much of which his syndicates own. ''New York has been wonderful to me,'' he said quietly. ''It has presented opportunities that I doubt I could ever have found elsewhere. I think New York is the greatest city in the world.''

It was a risk, but it seemed to have Brazil's inflation-beset economy on the right track at last. An induced recession, which in 1981 produced the first shrinkage in gross national product Brazil has had in modern history, brought significant gains and soaring hopes for 1982. Those hopes had been a growth rate of 5 percent compared with minus 3 percent in 1981; inflation of 75 percent, down from 1981's 95 percent; a trade surplus of $3 billion, $2 billion more than last year; an inflow of $14.5 billion in foreign funds, down from nearly $16 billion in 1981, and foreign reserves of $8.5 billion. But with the midyear figures in, the hopes have been shattered. The inflation rate, retreating earlier this year, went on the offensive again, registering a jump of 8 percentage points in June and 6.1 points in July. In the 12 months ended July 31, the inflation rate was 99.5 percent, and a triple-digit level seems unavoidable.