A District lawyer, a Bethesda gem dealer and six others have been indicted by a federal grand jury in Atlanta on charges of participating in a fraud scheme to sell cheap sapphires, emeralds and other gems for 30 to 40 times their actual value to unwitting customers in the Washington and Atlanta areas.

During an FBI investigation into the alleged scheme, undercover agents in Washington posed as prospective customers interested in selling expensive cars, including a Mercedes Benz and a Datsun 280Z sportscar, in exchange for gems, FBI officials said yesterday.

Washington attorney Floyd W. Anderson, 42, and the Bethesda gem dealer, Lawrence Andrew Funt, 29, were charged with conspiring and helping an Atlanta man, Jerry T. Melton, 43, who briefly worked from two residences in Washington and Kensington and ran a telephone "boiler room" operation from his Kensington home to solicit customers, according to the indictment.

FBI officials yesterday declined to say how much money had been obtained in the alleged scheme or reveal the number of people who may have been defrauded. They said, however, that they felt they had stopped the operation in its early stages.

In at least one case, a woman FBI agent posed as the wife of a Washington area man who had been approached by one of the participants in the scheme. In addition to cars, the participants attempted to trade the gems for real estate and cash, according to the indictment which was returned earlier this week in Atlanta.

A Beverly Hills gems dealer, who also was indicted, allegedly would certify to prospective customers in the D.C. area that his independent appraisal of gems offered for sale was $75,000 when actually he knew that they were worth less than $2,500, according to the indictment.

Melton, who also used the name of Jim Thompson, would sell several different false stories to various customers about the gems' origins, including that they were the ramining part of an $11 million collection he inherited from his grandmother, according to the indictment. He allegedly said that economic pressures were forcing him to sell the gems below their real value.

Prospective customers also were told that Melton sold parts of his "rare" collection for a $1 million Lear jet, that they had been shown to Hollywood movie stars and that Melton owned an art gallery, the indictment said.

Melton, who is facing separate federal charges in Atlanta for another alleged fraud involving the sale of hosiery products, was adjudged involuntarily bankrupt last year. He subsequently moved to the Washington area.

According to the indictment, Anderson, aware that the gems were being sold for inflated prices, agreed to meet with prospective customers "to substantiate the 'pitch' used by " Melton, advised Melton on the phony gem appraisals and allowed his law offices at 1850 K St. NW to be used for the transactions.

Anderson is also under investigation by a federal grand jury in Washington that has been probing physicians and lawyers allegedly involved in schemes to submit phony medical insurance claims arising from car accidents, according to papers filed in U.S. District Court here. Police seized cancelled checks and other records during a search of Anderson's law offices last September, according to court records. No charges have been filed in that case.

Funt, the indictment says, agreed to help Melton find inexpensive gems that coule be passed off as valuable.

Anderson could be reached for comment yesterday but Funt said he was innocent. Both have been released from custody on their personal bond. Melton is in jail in Atlanta under $200,000 bond.

The Atlanta grand jury indicted Anderson, Funt, Melton and the others on one count of conspiracy and nine counts of wire fraud.

Agents said most of the activity here took place last spring, but that the plan fizzled when the alleged members of the scheme became suspicious after Melton in his bankruptcy case last April.