A supervisor at the D.C. Bureau of Motor Vehicle Services and a city used-car dealer were indicted here yesterday on federal conspiracy and bribery charges in an alleged scheme in which temporary and dealer car tags were sold illegally and at inflated prices.

Joseph W. Gant, 61, of 2405 Savannah St. SE, a bureau employe responsible for investigating used-car dealers' use of the special tags, and James C. Rettaliata, 62, of Baltimore, who operates Car Plaza in the 600 block of New York Avenue NW, were each charged in the indictment with two conspiracy counts. In addition, Gant was charged with five counts of accepting bribes and Rettaliata was charged with five counts of paying bribes.

Prosecutors said the alleged scheme involved more than 100 illegal sales of "X," "DX" and "D" special tags, vehicle salesmen's licenses and safety inspection stickers, and continued for more than four years before the two men were arrested in November.

According to the indictment, three types of transactions were involved in the overall scheme:

*Sale of special temporary tags, at prices ranging from $20 to $50, to persons who could not afford the normal registration cost for a car or who did not have proper insurance. In some instances, purchasers of used cars from Car Plaza had not completed paying the full purchase price, and the dealership would not give them the title needed to register properly. Such tags normally cost no more than $10, and are sold only by the Bureau of Motor Vehicle Services.

*Sale of salesmen's licenses, usually for about $150, and temporary dealer's tags, at rates of as much as $150 a month, to persons who wanted to buy cars for their own use at wholesale car auctions. Under city policy, a used-car dealer may normally obtain one dealer tag per officer and two per salesmen at a cost of $53 for the first tag and $19 for each additional tag.

*Sale of safety inspection stickers, usually for $100, to persons whose cars could not pass city safety tests.

Each of the conspiracy counts carries a maximum sentence of five years in jail and a fine of $10,000, and each of the bribery counts carries a maximum sentence of 15 years in prison and a fine of $20,000 or three times the amount of the bribe.