The recent Social Security trustees' report, which said the old-age and disability trust funds should remain in sound shape well into the next century, revealed that the maximum Social Security tax could rise steeply in the next few years -- from $2,791.80 this year to $3,947.40 in 1990.

The report contained a table projecting the increases in the maximum taxable wage under Social Security, which rises automatically each year at a rate corresponding to the annual growth of the average wage. This makes it possible to calculate what the likely tax bite will be for the highest-paid workers, using the projections and the schedule of Social Security tax rates enacted in 1983:

For 1985, the worker's tax rate is 7.05 percent and the maximum taxable wage is $39,600, producing a tax of $2,791.80.

In 1986, the rate will be7.15 percent and the maximum taxable wage is projected to be $41,700, producing a tax of $2,981.55. The actual maximum taxable wage will be set later this year.

For 1987, the rate will be 7.15 percent and the maximum taxable amount projected at $43,200, for a top tax of $3,088.80.

For 1988, a rate of 7.51 percent on a maximum base of $45,600 would result in a tax of $3,424.56.

For 1989, it will be 7.51 percent and $48,600, for a maximum tax of $3,649.86.

For 1990, it will be 7.65 percent and $51,600 for a maximum tax of $3,947.40.

Then there will be some respite, since the tax rate will stay at 7.65 percent, but the maximum taxable wage will continue to rise, although the amounts haven't been projected.

MORE DOCTORS . . . A study by the Public Health Service's Bureau of Health Professions estimates that the number of active doctors will rise to 594,600 in 1990 and 706,500 in the year 2000, compared with 326,200 in 1970, 467,000 in 1981 and 527,900 today.

Of the total projected at the end of the century, 94.5 percent will be doctors of medicine, the rest doctors of osteopathy. By the year 2000, it is projected that there will be 260 physicians for each 100,000 people, compared with 199 in 1981 and 217.8 in 1985. Four-fifths of the total in 2000 will be trained in the United States, compared with 77.5 percent in 1985.

The bureau estimates that the proportion of female doctors will rise from 14 percent today to 20 percent by 2000.

The fastest-growing specialist groups are expected to be gastroenterologists, diagnostic radiologists, pulmonary disease specialists, pediatric cardiologists and neurologists, all of which are expected to double their ranks between 1981 and the end of the century. The number of physicians specializing in public health, on the other hand, is expected to drop from 2,520 in 1981 to 1,290, a 49 percent decline. The number of pediatric allergists is expected to drop by 18 percent and occupational medicine specialists, 19 percent.

EXPENSIVE PATIENTS . . . The 5 percent of hospital patients who have catastrophic high-cost illnesses account for nearly a third of hospital costs, according to a report prepared by University of Michigan researchers for HHS's National Center for Health Services Research.

The study, based on 586,319 patients discharged from Maryland's 54 acute-care hospitals in 1981, considered an illness to be a high-cost catastrophic condition if a patient's costs exceeded $7,500. It found that 5 percent of all discharges fit that description and that they accounted for 30 percent of total charges. Costs for a patient's care ranged as high as $276,632.

The research center said about two-thirds of the high-cost cases occur in teaching hospitals. It said Medicare covers about half of all high-cost cases, Blue Cross about a quarter, private insurance about10 percent and Medicaid about 9 percent. But in 5 percent of the cases, patients and their families had to pay for the care out of their pockets.

TEEN SUICIDES . . . Some 5,025 young people between 15 and 24 committed suicide in 1982, a 66 percent increase since 1971 that now makes suicide the third leading cause of death in that age bracket, according to Secretary Margaret M. Heckler. So she has named Dr. Shervert Frazier, director of the National Institute of Mental Health, to head a new Task Force on Youth Suicide. The department also is sponsoring a national conference here on youth suicide June 19-20.