IN THE SUMMER of 1787, Catherine the Great of Russia was entertaining a group of high government officials and distinguished foreign guests, including Emperor Joseph II of Austria. Part of the entertainment was a cruise down the Dnieper River to show off all the new settlements in the Black Sea area. There was only one trouble: there were no settlements. Ever ready to improvise, Catherine's lover, Field Marshal Grifori Potemkin--sort of an 18th century Walt Disney--constructed sham villages along the riverbank, hired a few peasants to wave at the floating royals and saved the day.

Someone in the Treasury must have heard of this Russian technological advance, for it was announced this week that the Secret Service will build a Potemkin White House in Beltsville. The objective is not to fool visiting heads of state, but rather to train Secret Service agents and to familiarize them with the physical aspects of the White House, Blair House, Pennsylvania Avenue and Lafayette Park. For a mere $1.6 million, movie-set facades will be constructed at the Secret Service training center in Prince George's County. This is a really marvelous idea for at least three reasons.

First, news of this venture should give the sagging housing market a boost. New home construction is at an all-time low, but once postponing purchasers and despairing developers learn that there is a market for multi-million dollar single-family dwellings --even without rooms, floors and ceilings--morale should go way up. It's just a matter of creative financing, of course. With a rich uncle, the Beltsville builders don't even need a mortgage.

Second, the White House set has tremendous tourist potential. Universal Studios makes a fortune busing tourists around old "Gunsmoke" and "Alien" sets. Why can't the annual springtime congestion around 1600 Pennsylvania Avenue be abated by transporting some visitors to the suburbs to see the mock-up? As an added inducement, the Park Service could hire a team of president and first lady look-alikes--the kind who hire out for shopping center openings--to wave from the balcony. And Rich Little could tape a greeting: "Weeell folks, welcome to President-o-rama." There are big bucks in the proposal, and the Treasury should be thinking about exploiting the potential.

Finally, the whole Potemkin White House idea may have an application to our defense establishment. It is very reminiscent of the old MX-missile race track basing system. Only instead of just two White Houses you would have 60, and the Russians would have to guess which one the president was in.

Can the Secret Service really be serious about this?