Salaries of scientists and professionals rose 5.2 percent in 1984, the smallest increase in a decade, Wyatt Co. reported yesterday.

Even so, the 161,503 employes at 1,356 firms covered by Wyatt's survey did better than other workers. The Labor Department found that increases for all full-time wage and salary workers, not just scientists and professionals, averaged 4.3 percent.

Wyatt, a large actuarial and employe-benefits consulting firm that conducts an annual survey of professional, administrative, scientific and engineering personnel, said the overall increase of 5.2 percent was the lowest in the decade that Wyatt has been conducting the survey. Wyatt's figure for the preceding year was 5.6 percent, and the high was 9.6 percent from the 1980-81 period.

Among professional, administration, scientific and engineering employes, the biggest salary increase -- 5.9 percent -- was for medical and legal personnel employed by the firms surveyed. The survey did not cover medical and legal personnel in private practice.

Salaries for workers in human resources jobs rose 5.7 percent over the year covered by Wyatt's survey, March 1984 to March 1985. In aviation, the figure was 5.6 percent; in data processing, 5.5 percent; in accounting and financial categories, 4.9 percent; in engineering, drafting and designing, 4.8 percent, and in scientific jobs, 4.6 percent.

William Frymoyer, compensation consultant in Wyatt's Chicago office, said, "The market forces of supply and demand are influencing professional and scientific salaries. There is a plentiful supply of highly qualified personnel, especially visible among the lower job ranks, which, joined with already uncertain conditions and low inflation, is keeping salary growth to a minimum."

Underscoring his reference to declining inflation as a partial explanation for low professional and scientific salary growth, Wyatt's figures show that the salaries generally rose the most in periods of high increases in the consumer price index and the least in periods of low CPI increases.

For the past three years, as inflation has been low, increases in salaries have been slowing down but still are outpacing the CPI.

The new Wyatt figures showed that salary increases were highest in the Northeast -- 5.5 percent. They were 5.2 percent in the North Central states, 4.9 percent in the Southeast, 4.8 percent in the West and 4.7 percent in the South Central states.

Frymoyer said the higher increases in the Northeast reflect the the "relative stability and prosperity" in the East Coast area.