A Washington firm accused of defrauding investors in Mexican pesos agreed yesterday to give customers their money back and to close down its "peso pool" that promised investors "mathematically astronomical returns."

The Commodity Futures Trading Commission said Capital Cities Currency Corp., which has offices at 1901 Pennsylvania Ave. NW agreed to the terms to settle a CETC complaint filed in U.S. District Court last week.

Capital Cities, the CFTC charged, collected more than $174,000 from investors in a commodity scheme that failed to disclose risks to investors and violated several other federal regulations.

Continuing its crackdown on illegal commodity investment plans, the CFTC yesterday made public two major cases involving alleged illegal gold and silver schemes.

The agency said it has filed administrative complaints charging three firms with illegal sale of commodity futures contracts. Named in the complaints was Monex International Ltd., of Newport Beach, Calif., one of the nation's biggest dealers in gold investments; First National Monetary Corp. of Southfield, Mich., and Trending Cycles for Commodities Inc. of Miami Beach, Fla...

In all three cases the companies sold what they called "forward contracts" for gold and silver. The CFTC charged the contracts were thinly disguised futures contracts, which can legally be sold only on federally regulated exchanges.

All three firms could be banned from the commodity business or subjected to other sanctions from the CFTC if an administrative law judge upholds the complaints.

In another case yesterday, the CFTC lawyers asked a federal judge in Florida to issue an injunction to halt what they said was the biggest illegal commodity option sales operation in the nation.

The agency charged that 240 customers in 37 states were victimized by a group in Florida companies known as International Gold Exchange Inc., International Gold Bullion Exchange Inc., Centennial Marketing Co. and Center Marketing, all with offices in the Miami area.

The CFTC complaint charged that in 11 months, IGE collected $2.29 million from customers and paid out only $862,000 in cash or gold. The complaint accused the Florida companies of operating "a classic Ponzi scheme" in which fees collecred from new customers were used to pay off previous investors.

The companies claimed they had large quantities of gold in Swiss banks, the CFTC said, but in fact they bought only small amounts of gold from Florida dealers to cover initial deliveries to customers.