The Fourth U.S. Circuit Court of Appeals in Richmond ruled yesterday that the Marriot Corp. illegally deducted tips from federal minimum wages it paid to waiters and waitresses at its Joshua Tree restaurant in McLean and ordered the company to reimburse the employees double the minimum wages they had earned.

Marriot Corp. attorney Ivan Rich said the decision will effect about 30 employees who worked at the restaurant between July, 1974, and June, 1975, but said he does not know how much the back wages will be. He said he did not know if Marriot plans to appeal the decision, which upheld an earlier ruling in U.S. District Court in Richmond.

The court's decision will make effective a similiar ruling last November. U.S. District Court Judge Albert V. Bryan in Alexandria ruled that Emersons Ltd., will have to reimburse about 700 employees between $148,000 and $149,000 in back wages from May, 1974, until last October, according to U.S. Department of Labor lawyer James B. Leonard.

Under the two restaurants' policies, waiters or waitresses would give management daily the equivalent of the minimum wage from their tip money. The restaurant then would pay employees weekly the minumum wage. Thus the restaurants were able to pay nothing out of their own pockets to employees, according to sources familiar with the cases.

Under the Fair Labor Standards Act of May, 1974, only half of the hourly minimum wage can be credited from tips to pay an employee's salary.