If you order fresh shrimp or Idaho potatoes from a menu in the District of Columbia now, chances are that is precisely what you will get, the D.C. Department of Environmental Services reported yesterday with obvious satisfaction.

The department said its six-month "truth in menus" crackdown that began last July has been successful and will continue.

In a study in 1977, prior to the heavily publicized crackdown, the department found such discrepancies as turkey used to make chicken salad, domestic ham or cheaper cuts advertised as imported ham, frozen seafood listed as fresh and Idaho potatoes coming from almost everywhere else.

That study found disparities in nearly 85 percent of all establishments that were checked, with an average of five disparities in each place and as many as 26 in one of them.

Bailus Walker, the department's environmental health administrator, said the new study found disparities in 49 percent of the establishments, with only two disparties in each place and more than eight in the unidentified restaurant that was the worst violator.

Walker said the department had issued a menu dictionary to help restaurant managers prepare their menus, and assesses demerit points during sanitary inspections when it finds disparties.