June 10, 1984

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.)