The cost of mailing a letter will go up by a penny early next year, the Postal Service's governing board announced Tuesday.

The new rates, approved by the independent Postal Rate Commission on May 11, will take effect Jan. 10, 1999, board chairman Sam Winters said. The new rates will boost the cost of mailing a first-class letter by one cent, to 33 cents. A variety of changes will affect other classes of mail."This penny increase is the right amount at the right time," Winters said at the postal governors' monthly meeting. "The rate adjustment is being made to provide a continuing investment in America's communications future," he said.

Other changes included include a cut in the price of sending additional ounces of first-class mail from 23 cents to 22 cents. Thus, a 1-ounce letter will go up to 33 cents, 2-ounces will be the same as now, totaling 55 cents, and heavier letters will cost less than at present.

In other typical price changes, a priority package will rise from $3 to $3.20; sending a local newspaper will cost 15.7 cents, up from 14.5 cents; the price to mail a magazine will rise from 27.1 cents to 29.1 cents and a basic parcel post package that cost $2.42 to send will rise to $2.74.