What was going on when I was born?

The Government began carrying out the second stage of its peace plan today, sending bulldozers and earthmovers to rip out the remaining earth and sandbag barricades of the so-called Green Line between the Moslem and Christian sectors of the capital. The immediate purpose was to neutralize the line, a 10-mile stretch of shattered buildings, barricades, wrecked cars and snipers' nests that separated Moslem West Beirut from Christian East Beirut. Units from the Third Brigade, made up of Moslems and Christians, are to take up positions along the line. The Moslem Sixth Brigade is to remain in West Beirut and the mostly Christian Fifth Brigade is to stay in East Beirut. Now a United Lebanon' ''There is no longer East nor West Beirut,'' the army commander, Brig. Gen. Mohammed al-Hajj said early this morning. ''It's now a united Lebanon with a united capital.''

Frank Corsaro has been staging operas of all kinds since 1958, but he was long reluctant to tackle ''Carmen.'' Not only did he find its form and story problematic, but its accumulated production traditions seemed to have created an impenetrable carapace around the work. ''Talk about warhorses!'' exclaimed the director recently. ''This is The Warhorse . It's an opera and it isn't an opera - it's sort of a French opera-comique and a zarzuela. It's story line is so tired, with the gypsy vamp and the garrisons, and with all those hit tunes it really seemed to belong in the old 'Vagabond King' operetta tradition.'' Mr. Corsaro is fascinated by the recent resurgence of interest in ''Carmen.'' But the rash of films and the much-discussed Peter Brook adaptation that played last season at the Vivian Beaumont Theater haven't addressed his problems with the work.

IF the James River Corporation has X number of 14-ounce soda cups in its warehouses, how long will they stay there before being transported to a Wendy's restaurant? Joe Hajla, an algebra teacher at New Canaan High School, spends the school year posing such questions to his students. This summer, Mr. Hajla himself has been assigned the problem. The question is part of a data base project he has undertaken in an experimental program to find useful summer work for Connecticut public school teachers, who often resort to such jobs as construction or house painting to supplement their salaries.

The Summer Games of the XXIII Olympiad, the first Olympics produced by private enterprise, began today under a brilliant afternoon sky with lavish opening ceremonies and a cast of thousands. Culminating the emotional ceremonies, Gina Hemphill, granddaughter of Jesse Owens, who won of four gold medals in the 1936 Olympics, ran out of a tunnel in the Los Angeles Memorial Coliseum, holding aloft a flame brought from Greece. 6 Years' Work for 16 Days Miss Hemphill ran one lap around the Coliseum track and handed the torch to Rafer Johnson, the American gold medal winner in the 1960 Olympic decathlon. He carried it up a staircase at the opposite end of the Coliseum and lighted a flame above it that is to burn throughout the 16 days of the Summer Games. After almost six years of preparation, this city, bedecked with bunting and finally gripped by Olympic fever, seemed ready for the Games, which have drawn more than 7,000 athletes from 140 countries. The number of countries competing is the largest in Olympic history, despite the decision by the Soviet Union and most other Communist countries to withdraw.

White Plains is a boom town by anyone's standards, with both commercial and residential development currently at its peak. According to David Ornstein, commissioner of the city's Planning Department, some developers have put their efforts into high-rise residential, hotel and office projects in the bustling downtown area, but new construction has also spread out into other neighborhoods.

TOUGH GUYS DON'T DANCE By Norman Mailer. 229 pp. New York: Random House. $16.95. THE first question is, Did Tim Madden, drunk and drugged, murder Jessica Pond? If not, who did? And in any case, how did Jessica Pond's severed head turn up in Madden's marijuana patch in Truro? Norman Mailer's new novel is a murder mystery. The scene is Provincetown, Mass., on Cape Cod - ''And for fall, winter and spring, nothing is superior to little old P-town'' - the time is November, all the visitors have gone. Madden, an ex-bartender, is a writer of sorts. He has also done three years in jail for drug-running. His wife, Patty Lareine, has left him, so he is hitting the bottle in The Widow's Walk bar. Things get blurred when he blunders into a conversation between a California lady and her sexually ambiguous escort. In no time at all another female head turns up, severed and blond - ''Any lady who chooses to become a blonde is truly blonde,'' according to one of the novel's more charming passages. Two hundred pages later we have assembled, by my count, seven corpses, not including Madden's dog, Stunts, killed by Spider Nisseh's knife.

The Games of the XXIII Olympiad began tonight with spectacular and colorful opening ceremonies and two final torchbearers instead of one. Most of the 7,000-plus athletes from 140 nations marched in an 80-minute parade, many resplendent in native costumes. There was entertainment by 12,000 dancers and musicians. There was live and recorded music, pennant waving and a magnificent card stunt. And there was more excitement for the capacity crowd of 93,000 that sat through 80-degree heat in the Los Angeles Memorial Coliseum. Tickets cost $50 to $200, and the show seemed well worth it.

I bumped into Benson, a fellow actor, in the grocery recently. His normally brown hair was several shades of puce and he was wearing a woman's raincoat. When he saw me he waved and pointed to his shopping cart, which was filled with balls of angry green wool. ''Isn't this great?'' he shouted. ''Twelve balls for a dollar!'' It seems he was planning to crochet tablemats for Christmas presents.

When Walter F. Mondale stood at the podium of the Democratic National Convention July 19, with the cameras of the three broadcast networks, the Cable News Network and hundreds of local television stations trained on him, the hall in which he stood, San Francisco's Mosconi Center, had been turned into a huge television studio, a vast showcase with one purpose: to take the candidate's image to as many viewers as possible. ''It is time for America to have a season of excellence,'' Mr. Mondale said, raising his voice for the microphones, raising his chin for the cameras as he called for a stiffening of the American resolve. ''Parents,'' he said, ''must turn off that television.'' A roar went up from the audience.

BRIDGEPORT B RIDGEPORT Mayor Leonard S. Paoletta says that people in the suburban towns surrounding Bridgeport do not appreciate his city and all that it does for them. He says they should not just appreciate his city, but should show it with donations from their local budgets. ''We are there for those people,'' said the Mayor, adding, ''they don't have the slightest thought in their minds that they are indebted to us.'' The Mayor singled out residents of nearby Fairfield, Stratford, Trumbull, Easton and Monroe as being quick to ''malign'' the state's largest city. ''They don't want to be identified with us,'' he said.

WASHINGTON SENATE and House negotiators struggled last week to strike a compromise on one of the major issues still facing Congress, an authorization bill outlining the Pentagon's budget for the next fiscal year. By week's end, the talks seemed to be bogging down, and one of the negotiators, Representative Les Aspin, Democrat of Wisconsin, muttered, ''I'm discouraged. The deal now is not looking very good.'' One reason for the stalemate, he added, was the paralyzing effect of election-year politics. ''Party positions are getting harder,'' he said, ''and I don't know if we want an agreement at any cost.''

The Mets' seven-game winning streak came tumbling down yesterday when the Chicago Cubs scored eight runs in the eighth inning and buried them, 11-4. More than that, Ron Darling also failed for the fourth straight time to win his eighth straight game. Doug Sisk, one of the stoppers of the bullpen, failed to stop anybody for the second game in a row. And the Mets, after rallying for a tie in the seventh inning, promptly lost the glow in the eighth and suffered their worst inning in two and a half months.