Prostitution rings are providing young boys to male customers in Washington and are reportedly selling information about their clients' sexual preferences to foreign intelligence services, a private investigator testified yesterday.

The investigator, Dale Smith, who works for the New York State Senate's Select Committee on Crime, said he had learned that British, Israeli and Soviet agents had bought information from several call services in Washington.

Mr. Smith appeared before the committee at the opening in New York City of a two-day hearing on prostitution among young males and on pornography.

Mr. Smith said that an accountant for five call services had told him about the sale of information to foreign agents. He refused to elaborate on the allegations when questioned by reporters, but the committee counsel, Jeremiah McKenna, said that the information concerned ''government officials.'' He declined to be more specific. Profit in Information