What was going on when I was born?

IN Freeport, Texas, the Dow Chemical Company early this year completed a new power plant that provides one million kilowatts of electricity - enough to light up Salt Lake City - and huge amounts of steam to manufacture chemicals. That gave the local utility a double headache: Not only was it deprived of a major customer, but under a stiff new law, it must buy back excess electricity from Dow. In Freehold, N.J., the local Y.M.C.A. last month started up a small engine, powered with natural gas, that simultaneously generates 70 percent of the 'Y's' electricity and all of the heat for its rooms, showers and swimming pool. The estimated savings will be $50,000 this year alone - and the engine itself only cost $130,000. In El Cajon, Calif., near San Diego, James A. Trent has a similar but much smaller engine alongside his stucco home. It has provided all of the Californian's electricity and hot water since 1982, at a saving in utility bills of $1,000 a year.

INDIVIDUALLY and in new coalitions, corporations in New Jersey are increasingly focusing on reining in the costs of their health-care benefit programs. Although no figures are available on how much employers in the state pay for group health plans each year - the nationwide total is around $75 billion - executives from across New Jersey say that their companies' health expenditures have been rising by 10 to 20 percent a year. In a survey conducted last year by the New Jersey Business and Industry Association, executives of 1,200 companies ranked health costs as their third-biggest problem - after the cost of workers' compensation and state business taxes and ahead of energy, environmental controls and general inflation. Some corporations simply have cut back their benefits or shifted more of the cost to their employees by asking workers to contribute more toward premiums and by increasing deductibles and co-payments for medical care and hospitalization.

LAWRENCEVILLE THE June Opera Festival of New Jersey will begin its inaugural season here Friday with a new English-language production of Mozart's ''Marriage of Figaro.'' Performances will take place in an idyllic site, the 890-seat, air-conditioned Kirby Arts Center at the Lawrenceville School, three miles south of Princeton on Route 206. Friday's performance starts at 8 P.M. The festival, which runs through June 30, is under the artistic direction of Michael Pratt and Peter Westergaard, the co-founders. One-third of its approximately $300,000 budget has been covered by a grant from Merrill Lynch & Company.

The vast majority of domestic programs begun by the Federal Government in the past three decades have survived despite budget cuts made under the Reagan Administration, according to a detailed study reported yesterday. The study, by the Woodrow Wilson School of Princeton University, found that in many cases the states had replaced significant amounts of the lost Federal money as programs were placed under their control. Working Poor Lose Benefits One major exception, according to a 700-page report, was the program that extended welfare benefits to the working poor. President Reagan, in an initiative approved by Congress, succeeded in removing the working poor from the rolls in most states. The study, conducted with money from the Ford Foundation and other private sources, is the most detailed of several that have tried to measure the effects of Reagan policies. Most of the others have examined particular aspects of the policies.

The leaders of the seven major industrial democracies pledged today to make it easier for some of the hard-pressed third world countries to repay their debts, promised to continue their own vigorous policies against inflation and voiced their support for ''precise commitments'' to the ''nonuse of force'' by both East and West. In a long economic communique and three shorter political statements issued at the end of the 10th economic summit meeting here, President Reagan and six other government leaders touched on most of the issues they had discussed, but there were signs that in several important cases they had been unable to agree on specifics. As the leaders concluded their deliberations at Lancaster House, tens of thousands of antinuclear demonstrators marched through the streets of central London, carrying banners and placards denouncing American policy. The organizers said more than 150,000 people took part. They were kept well away from the conference sites by the police, but traffic was paralyzed and more than 170 people were arrested for obstruction during the march and two smaller protests. (Page 13.)

People hunting for an apartment or a house during this peak home-hunting season have had two major concerns: getting soaked by record rains and being unable to afford increasing mortgage interest rates. Long-term mortgage and cooperative loan rates in the metropolitan area, which have risen a little every week since the middle of February, are now up by more than 1 percentage point for the period and are approaching 15 percent. Short-term rates also have risen, but many lenders have absorbed most of the increase by continuing to offer introductory discounts on mortgages that have annual rate adjustments. If rates remain high next year, however, borrowers may see their 9 1/2 or 10 percent adjustable loans jump 2 percentage points or higher, depending on whether the mortgage has a limit on the amount of the first adjustment. The rate increases mean payment increases. The monthly cost of an $80,000 conventional mortgage originated on Feb. 17 was $901.87; the same mortgage taken out on June 1 carried a monthly cost of $978.37, according to HSH Associates of Pequannock, N.J., which provides consumers with competitive rate information on lenders. The first year's monthly payments on an $80,000 adjustable-rate loan, according to HSH, increased from $759.44 to $795.90 in the same period.

M OSLEMS against Hindus, Assamese against Bengalese, Sikh terrorists against all the rest - in India the sources of conflict that threaten the unity of the world's largest democracy seem endless. Last week, a long-running conflict between the Government and the Sikhs of Punjab, one of India's most advanced states, appeared to reach a point of desperation. Some 450 Sikh terrorists and more than 80 soldiers died as the army assaulted the Golden Temple of Amritsar, the holiest shrine of a holy city, and other religious centers.

Gary Hart declared today that he would continue his candidacy for the Democratic Presidential nomination and reminded delegates that under party rules, they are free to switch to him from Walter F. Mondale. But, in an apparent acknowledgement of the urging by party leaders that he tone down the conflict with Mr. Mondale, the Colorado Senator said, ''I will do nothing to hurt the Democratic Party and I will do everything to achieve a Democratic victory in 1984.'' Direct Criticism Avoided In a carefully prepared speech delivered to about 3,000 delegates attending the state Democratic convention here, Mr. Hart avoided direct criticism of Mr. Mondale by name, another signal that he was shifting his campaign emphasis away from personal confrontation and toward broad issues. There were implied criticisms of the former Vice President, however, as Mr. Hart sounded the main themes of his candidacy, saying that the party needed new leadership and to break the hold of interest groups.

''Art isn't easy,'' sings a character in ''Sunday in the Park with George.'' ''Having just the vision's no solution,/ Everything depends on execution./ The art of making art/ Is putting it together/ Bit by bit . . .'' Putting together a Broadway musical, of course, is itself a highly strenuous art. Bit by bit, a show is assembled, piece by piece it emerges - the product of talent, hard work, carefully calculated choices and the fortuities of luck and timing. In the case of ''Sunday,'' the new Stephen Sondheim-James Lapine musical, the process took two years and involved an Off-Broadway workshop, as well as hectic revisions during rehearsals and previews. The story of that process is, at once, a story about the dynamics of collaboration between two gifted artists; and a story about how a work of art evolves from a few phrases jotted down on a yellow legal pad into a fully realized show, from a troubled production - with morale problems and poor word-of-mouth during previews - into a Broadway hit that has won both critical acclaim as a ground-breaking musical and popular support.

Martina Navratilova overwhelmed Chris Evert Lloyd for the 11th straight time today, winning the French Open final in 63 minutes, 6-3, 6-1. In doing so, Miss Navratilova earned a bonus of $1 million and a somewhat grudging recognition as the third woman to capture the four Grand Slam events in tennis. Miss Navratilova took control in the fourth game, as she caught Mrs. Lloyd out of position, particularly by using the drop shot, and forced her to scramble. Mrs. Lloyd, the longtime world's No. 1 player until displaced by Miss Navratilova, paid tribute to her conqueror, saying: ''I couldn't find any weaknesses. I couldn't anticipate the drop shots, I couldn't read her. She took advantage of making me run forward, and I wasn't quick enough. She is playing the best she has ever played. I don't know how much better she can get.''

It took less than 15 minutes for Hoboken's unused Sadie Leinkauf school to be sold for $1.2 million at a public auction last month. The auction was criticized by some residents, however, because the only condition the city imposed on bidders was that the building be used for housing.

On a 5.8-acre peninsula, itself on the Shippan Point peninsula in Stamford, the Collins Development Corporation is creating a ''dockominium,'' a colony of 78 apartments and 140 pleasure boat slips in which both kinds of accommodations will be sold as condominiums. ''Dockominiums,'' in which buyers live just a few steps from their boats, have gained in popularity in recent years, but their development has been slowed in Connecticut by restrictions on waterfront building imposed in 1980.