Many of the professionals who M got out from under the District of Columbia's income tax as a result of a court decision last year now will have to pay a city license fee instead_ if the D.C. Finance and Revenue Department has its way.

The background: In 1975, the D.C. City Council passed a law requiring lawyers, doctors, writers, accountants, consultants and others who did business in the District -- regardless of where they lived -- to pay local taxes on their professional incomes.

In 1980, the D.C. Court of Appeals ruled that this violated a congressionally adopted Home Rule Charter provision outlawing an income tax on nonresidents. That forced the financially pinched city government to refund more than $36 million to those affected, most of whom are suburbanites, who had paid it over a three-year period.

Now comes the city Finance and Revenue Department with an announcement that those individuals, with a few exceptions, who earn more than $12,000 a year from conducting what is described as "a trade, business or profession" must apply for a license by Dec. 1 to operate in the calendar year 1982. That includes city dwellers and suburbanites alike.

The license costs $25 a year, which is cheap compared with the penalty of $300 a day for violation. For a license application, call 727-6170 and ask for form FR 500-A. For information, call 727-6103.