Washington area investors who wanted to dabble in the foreign exchange or precious-metals market have been limited in recent years primarily to one company in town, Deak-Perera.

Ruesch International Monetary Services Inc. is betting that there is room in Washington for two foreign exchange companies and has set up an office downtown at 1140 19th St. NW.

A new American company with Swiss management, Ruesch specializes in foreign exchange and precious metals and represents the first competition for Deak -- for the past 10 years the area's only major specialist in foreign exchange and gold and silver.

"Competition will exist but I don't think it will be very serious," said the firm's president Otto J. Ruesch.

Ruesch offers a foreign currency certificate, the first of its kind, where the buyer does not have to take possession of the currencies, which are kept in a trustee account in a major Swiss bank.

Ruesch is very familiar with Deak, having served as a senior vice president in its New York office and heading its Washington office from 1969 to 1977. This is the company's first office, and plans are being made to open a Zurich branch and then gradually expand in the United States.

Ruesch cited a number of reasons for the decision to open an office in the District -- a 23 percent increase since 1976 in foreign nationals touring the United States, most of whom visit Washington; an increase in the number of Americans traveling abroad.