What was going on when I was born?

NASSAU Democrats, who were having trouble finding a candidate for County Executive, now have two men fighting for the nomination in what looms as a potentially damaging primary contest. John W. Matthews of Long Beach, a 43-year-old insulation contractor and vice chairman of the Nassau Democratic organization, was designated last Monday by the party's county committee to challenge County Executive Francis T. Purcell. However, Mr. Matthews faces a primary challenge in September from Assemblyman Lewis J. Yevoli, 42, of Old Bethpage, who is accusing his own party leadership of ''an insidious deal'' with Nassau Republicans. The contest, judging by the county committee meeting at the Salisbury Restaurant in Eisenhower Park, shapes up as one between a low-key, relatively inexperienced candidate and an aggressive, street-wise legislator.

The New York Mets lost a 4-2 lead in the eighth, then rallied in the bottom of the inning to score a 7-4 victory over the Los Angeles Dodgers at Shea Stadium yesterday afternoon. The Mets got four runs in the first two innings and entered the eighth with a seemingly safe edge. But Pedro Guerrero tied the game with a two-run home run off Neil Allen, the third of four Met pitchers. The homer was Guerrero's second of the game and fifth of the year.

Mr. Reagan's Tax Problem As the May 15 deadline for a joint budget resolution nears, support for the Administration's tax and budget cutting programs appears strong. However, many Congress-watchers remain convinced that compromise is inevitable when individual committees begin to pare their own budgets next month. Although last week's vote on the House budget proposal gave the White House a stunning victory, some economists say the Administration needs even more firepower. In light of recent indications of unexpectedly fast growth and rapidly decelerating inflation the President's program could use signs of renewed economic weakness in order to convince Congress the nation needs the Reagan tax cut program.

DEMOCRATS say they have more fun than anybody, and that seemed true enough last weekend at their annual fund-raising dinner at the Rye Town Hilton. But they are also more likely to encounter the unexpected, and that also was evident. The 600 guests, who paid $90 a plate, danced through much of the evening, heard appeals from politicians running for office, shared the jokes and nostalgia of such occasions - and then were lambasted by one of their honored guests, May Morgan Robinson, for failing to share political power with blacks. It began auspiciously enough with Representative Peter Peyser of Irvington, singing ''Pennies From Heaven'' and receiving enough applause for an encore, ''Carolina in the Morning.''

After less than four months in office, President Reagan has divided and transformed the once-powerful public officials' lobby, which for the last two decades constituted a united coalition in behalf of more Federal funds for a vast array of local governments and agencies in the Federal system. The President has secured support for his budget cuts among important organizations within the lobby, even though the cuts will result in less public services at all levels of government. Where he has not won support he has muted the opposition. His plan to give the states new authority in the use of Federal funds that have gone directly to local governments has renewed a divisive struggle between the states and the cities, which had reconciled their historic antagonisms when both were tapping new sources of Federal money.

Citibank has begun to move aggressively into the home-mortgage market in Westchester and Rockland Counties, signaling a new effort by commercial banks to expand their services to suburban consumers in an area historically the preserve of savings institutions. The move comes at a time when high interest rates and deposit withdrawals have curtailed the ability of savings institutions to offer attractive loan packages to potential home buyers. The commercial banks' move benefits home buyers by making more mortgage money available, although the individual borrower seeking the best possible terms often does well to shop from one institution to another. The Citibank ''Door Opener'' program in Westchester and Rockland Counties, announced last week, is the most ambitious move yet by a commercial bank to capture the suburban mortgage customer. It is aimed particularly at the flourishing corporate relocation market, which, according to Brian J. O'Hare, a Citibank vice president, accounts for up to half the home sales in the more affluent suburban communities in the New York region.

Preliminary plans have been filed in Greenwich for subdivision of the 1,468 acre Rosenstiel estate, one of the largest privately owned tracts of undeveloped land in the metropolitan Northeast. The property, also known as Conyers Farm, was bought last October by the Conyers Farm Partnership - Joseph Allen and Murray and Peter Brant -for $18 million. The bulk of the land is in north Greenwich, with 300 acres extending into New York State. Peter Brant is president of Riviere du Loup, a newsprint manufacturing company based in Greenwich. Mr. Brant's father, Murray, founded the company. Mr. Allen is a business associate. The young Mr. Brant also owns the 200-acre White Birch Farm opposite the Rosenstiel property on North Avenue.

Six members of El Salvador's armed forces have been arrested as suspects in the slayings of three American nuns and a lay religious worker last Dec. 2, Defense Minister Jose Guillermo Garcia announced today. ''They are only suspects,'' he said at a news conference here. ''I am not going to reveal their names or anything else for the moment.'' (The Associated Press quoted Mr. Garcia as saying that the suspects were arrested April 29. It said a document sent by the Salvadoran Government to the United States Embassy identified three of them as Sgt. Luis Antonio Colmindres Aleman and Cpls. Luis Elias Sanchez and Jose Roberto Moreno Canjara. It did not give their branch of the armed forces.)

THE Ridgewood Water Company, which serves four communities in Bergen County, was taken off rationing last Wednesday, along with 17 other water companies serving 36 towns. Harold Florence, the company's director, still does not know why Governor Byrne placed it on those mandatory controls last Feb. 7. ''It just didn't make any sense,'' Mr. Florence said the other day. ''There was no need to put us on rationing. It was very poorly done.'' Mr. Florence's company, which supplies 60,000 people in Ridgewood, Glen Rock, Midland Park and Wyckoff, has been in the same boat as several other small municipal water concerns that use groundwater wells. Many such companies elsewhere in Bergen County, as well as in Essex, Somerset, Morris and other suburban counties, were rationed last Feb. 7, when state officials were genuinely frightened about water supplies.

The Houston Rockets matched a statistic in the National Basketball Association record book today. It was not one they would like to remember. The Rockets, routed by the Boston Celtics, 94-71, at the Summit, tied the record for the fewest points scored by a team in the championship round since the 24-second clock went into effect for the 1954-55 season. The Syracuse Nationals were beaten, 74-71, by the Fort Wayne Pistons on April 7, 1955.

The two women sitting in the front of the Greyhound bus had spent much of the ride from Birmingham exchanging thoughts on a variety of subjects: life in Traverse City, Mich., and Youngstown, Ohio, the cities from which they came; their grandchildren; the rising cost of bus and plane fares, and what they hoped to achieve in the remaining years of their lives. Inez Lofton, 57 years old, is black; 45-year-old Jane Sisco is white. Twenty years ago, a black woman and a white woman sitting side by side in a bus in Alabama could have been subjected to physical abuse, arrested and even placed in jail. They would have been violating strictly enforced state laws against interracial contact that affected transients and residents alike. A few rows behind the women was John Lewis, who made the same journey two decades ago as a member of a small, racially mixed group who called themselves Freedom Riders, who were challenging such laws and customs in the South. Their efforts to integrate the bus facilities here were greeted by mob violence that shocked the nation.

A month ago, during their first-round Stanley Cup playoff series with the Boston Bruins, the speedy young Minnesota North Stars decided to grow beards as long as they lasted in the playoffs. Tonight the superstitious beards were still growing, however fuzzy and scraggly, as the North Stars advanced to the Cup finals for the first time in their 14 seasons in the National Hockey League, defeating the Calgary Flames, 5-3, at the Met Center. The victory clinched the semifinal playoff series for the North Stars, four games to two, and they will face the Islanders in the final series starting Tuesday night at the Nassau Coliseum. The North Stars, who finished ninth in the regular season and had defeated the eighth-place Bruins and the fifth-place Buffalo Sabres to get to the semifinals, eliminated the seventh-place Flames by shooting more often tonight, 35-26, and skating faster for most of the game. The Stars scored a goal in each of the first two periods, and took a 4-1 lead with less than six minutes left in the game, sealing their victory.