What was going on when I was born?

President Reagan, in an interview made public today, expressed doubts about future financing of Social Security. Mr. Reagan said in the television interview, filmed Monday, that he would never ''pull the rug out'' from under those now receiving Social Security benefits. But he said, ''There is a possibility - well, probability - that many people, young people now paying in, will never be able to receive as much as they're paying.'' He suggested that that was unfair.

Bicycle messengers, who have been accused of recklessness by city lawmakers, will be regulated for the first time under a bill signed yesterday by Mayor Koch. The measure was drafted after complaints to city officials that the cyclists endangered pedestrians, drivers and themselves by ignoring traffic laws. The new law requires commercial cyclists - those who deliver everything from groceries to legal briefs - to carry identification cards and to display their employers' names on vests, jackets or similar clothing. It also requires the employers to keep log books of where their cyclists go and when.

Text of statement, page 5. MOSCOW, July 6 - The Soviet Union today reiterated its offer to hold talks with the United States on banning arms in space, but appeared to add a precondition, calling for a mutual moratorium on testing. A Government spokesman said that such talks, which the Soviet Union has proposed for September, would be ''incompatible'' with the continued testing of space weapons. The spokesman's comments came at a news conference here after Tass, the official press agency, issued a new statement saying that Moscow's offer for negotiations to ban all types of weapons in space remained open.

The nation's unemployment rate fell by four- tenths of a percentage point in June, to 7.0 percent, the lowest level in more than four years, the Labor Department reported today. The June decline, the second consecutive large monthly drop in unemployment, was well distributed among all categories of workers: adults and teen- agers, men and women, and white, black and Hispanic people. Gains in Employment Coupled with a solid June gain in employment, the reduction in joblessness suggested that the economy continued to expand at a strong pace in June, a stronger one than the Reagan Administration expected. ''I would worry if it doesn't slow down further in the third quarter and fourth quarter,'' said Martin S. Feldstein, chairman of the Council of Economic Advisers. He was alluding to the possibility that the rising level of economic activity might cause inflation to acclerate.

Modern Israel, now 36 years old, is moving from the generation of its founding into the generation of its maturity without having resolved the most fundamental questions faced since its creation. In essence, they are the issues of what kind of a society this will be: religious or secular, nationalistic or humanistic, Western or Middle Eastern, absolutist or pluralistic. The struggles between these diverse qualities are intense; they are determining the nature of democracy and Judaism, the two key elements of Israel's fate. The writer of this dispatch has just completed a five-year assignment as bureau chief of The New York Times in Jerusalem. Some social thinkers believe that clear resolution of the conflicts is impossible and perhaps not even desirable because the varied population of Jews from throughout the world has remained intact partly because of the society's ambivalence. Its ability to sustain tension between opposing impulses has made room for variety. If the state became unequivocally religious, for example, the secular Jews would be alien, and if it became wholly secular, the religious would feel apart.

David Brower, a longtime leader of the American environmental movement, was dismissed this week as chairman of Friends of the Earth after refusing to cut the staff of the politically active group. Mr. Brower, who founded the organization 15 years ago and led its militant demands for environmentally sound solutions to the nation's fuel needs, refused to carry out staffing cuts ordered by the group's board of directors in seeking to resolve severe financial problems, officials said. To deal with a debt now totaling about $700,000, the board of directors recently decided to lay off a substantial portion of its 49-member staff, including its field representative in New York City. Rafe Pomerance, president of the group for the past four years, stepped down last week.

The Government economic policies that have drawn such praise from Mexico's international creditors were not on Jesus Sanchez's mind today as he sifted through the municipal garbage dump here, scavenging scrap to sell to feed his family. Nezahualcoyotl, just beyond the eastern limits of the capital, knew the meaning of austerity long before the word was made a battle cry of politicians. It is the type of place where making do with less often means making do without. Mr. Sanchez says that on an average day he can gather enough old bottles, cardboard and newspapers in his scuffed canvas sack to earn about 400 pesos, the equivalent of $2.16. It is enough to feed his family of eight with tortillas and chili, he said, but not much more. Last year there was milk nearly every week for the children; this year, with the price nearly two- thirds higher, it is a luxury.

Nigeria detained a British airliner in Lagos today in the aftermath of a kidnapping in London in which a wealthy Nigerian exile was seized at gunpoint, drugged and sealed in a crate ready to be loaded on a plane. The exile, Umaru Dikko, a former Government official who has been described as the Nigerian Government's ''most wanted man,'' was freed by the British antiterrorist police on Thursday night at Stansted Airport, 30 miles north of London. They broke open the crate just before the Nigerian Airways plane was due to take off. They found Mr. Dikko inside, drugged and unconscious, together with another man, who was conscious and equipped with drugs and needles.

When Hu Zuoling was sent to the Canton Prison for robbery, he disobeyed the rules and balked at work assignments, feigning illness. Now Mr. Hu has mended his ways. He works so hard at his prison job that he was able to return to his family the $45 they lent him when he began serving his sentence. Canton officials attribute his conversion to the prison's new responsibility system, which may be the most curious application yet of the economic incentives introduced in China five years ago by Deng Xiaoping.

The National Coal Board and leaders of Britain's 180,000 miners held a second day of talks Thursday on ways to end the four-month strike that has paralyzed two-thirds of Britain's coal industry. Meanwhile, striking miners, protesting plans to shut unprofitable pits and eliminate 20,000 jobs, blocked traffic in the Yorkshire market town of Selby and clashed outside the highly modernized pits there.

Rauf Denktash, the Turkish-Cypriot leader, said today that Greece was engaged in a secret military buildup on Cyprus and that he had asked the United Nations to stop such ''craziness.'' Mr. Denktash said he could confirm Turkish press reports that Greece was sending military personnel, arms and ammunition to the Greek-Cypriot southern part of the divided island.

The three leaders of Cambodia's resistance coalition ended three days of talks here today and said they had resolved to increase diplomatic and military offensives against Vietnamese occupation. A statement said the coalition president, Prince Norodom Sihanouk, the vice president, Khieu Samphan, and the prime minister, Son Sann, conducted their talks at the Prince's Peking home.