July 24, 1983

SUFFOLK COUNTY is catching up with Nassau County, at least as far as population is concerned. Sometime within the next 12 months, Suffolk is expected to draw even in the race. And while the number of people increase in the area, so do the number of elderly and one-person households, a trend that is similar to demographic changes taking place across the country, according to sociologists and governmental policy planners. The two-county area as a whole is expected to show a modest gain in its number of residents in 1983, reversing last year's trend, which showed a slight loss.

The Defense Department has recommended to President Reagan that he raise the number of American military advisers in El Salvador to 125 next year, more than doubling the current total, senior Administration officials said today. The Defense Department, according to the officials, has also proposed that the advisers be allowed to increase their mobility by accompanying Salvadoran forces into the field. But the department has recommended no change in the current policy that prohibits American servicemen from being involved in combat operations or working in combat zones. Mr. Reagan has the proposals under consideration but has not yet decided whether to approve them, the officials said. Some aides have warned Mr. Reagan that any rise in the Administration's self-imposed limit of 55 advisers in El Salvador could touch off serious opposition in Congress and might lead to the adoption of a legally binding limit.

''THE town is going to be discovered,'' Marguerite Dunscomb said regretfully, as she sat in a Somers coffee shop. ''As it is now, when you tell people where you live, they never heard of it.'' ''It will be good for the town,'' countered Patricia Testa, owner of Patty's Place. ''I've lived here all my life, and I get tired of this dead place.'' The two were considering what will happen two years from now, when two big corporations, International Business Machines and Pepsico, come to this rural town of 15,000 people.

The leader of the Druse minority in Lebanon announced today that he and a group of leftist and Syrianbacked leaders had created an alliance to oppose the Government of President Amin Gemayel. The Druse leader, Walid Jumblat, said the alliance, which he called the National Salvation Front, would administer areas in northern and eastern Lebanon now under the Syrian Army. Mr. Jumblat's forces have been engaged in heavy fighting near Beirut with Christian militia units of Mr. Gemayel's Phalangist Party. He said the front's leadership would consist of himself, former President Suleiman Franjieh, who is a Maronite Christian, and former Prime Minister Rashid Karami, a member of the dominant Sunni branch of Islam.

At a time when much of the rest of the country is trimming arts budgets and wondering whether major cultural institutions will survive, Texas is launching a new round of projects with huge price tags: a $75 million house for opera and ballet and a third major art museum in Houston, an art museum and a symphony hall in Dallas, and a music festival with aspirations to international stature in San Antonio. Is this just a matter of the ostentation of wealth -where money goes, culture will follow? Texas is proverbially rich, and the economic recession has hit the state belatedly and comparatively mildly, so the simplest explanation of the culture gusher is at least plausible - especially since These days, many of the Texans with the means to fund it, are beginning to consider culture not as a frill but as the potent sign of their own and their state's prestige. The push to make Texas a great cultural center is on - though the question of exactly how much actual creativity money can buy still remains.