When Harry Hughes enters office as governor of Maryland this January, he will inherit a $200 million budgetary surplus to help carry out his campaign promises of tax relief. Acting Gov. Blair Lee, III said yesterday.

Lee's latest fiscal forecast -- the size of the projected surplus has steadily grown with each prediction in recent months -- was based on unexpectedly high gains in traditional sources of state revenue, including sales and business taxes and the state's lottery game.

Several one-time windfalls have contributed to the expected budgetary bulge, Lee said. The largest of these is the $20 million worth of tax credits not claimed by eligible homeowners. In addition, there is $14 million in federal aid owed Maryland as support for social service programs.

Hughes, who will be inaugurated Jan. 17, promised during last summer's campaign to use any surplus to pay for $86 million in tax relief, including a nine-cent reduction in the state property tax and an increase in the standard deduction for state income taxpayers.

At his weekly press conference, Lee said the projected surplus does not indicate Maryland taxpayers are overtaxed. No one could have predicted that an upturn in the economy would coincide with the legislature's passage of a one-cent increase in the sales tax in 1976, he said.

"I'm sure you are all aware of Lee's law of budgetary surpluses," he told reporters. "The windfalls always come the year you don't need 'em. In a tight year, you don't get 'em."

Lee, who was defeated by Hughes in the Democratic gubernatorial primary election called for fiscal conservatism in the use of the surplus. He said the state's lively economy, which led to the current forecasts of a budget surplus for the fiscal year ending June 30, could easily go sour.