Reliance Group Inc. of New York revealed yesterday that it has bought more than 5 percent of the stock of San Juan Racing Association, owners of two Wasington Radio stations and a chain of other broadcasting outlets.

Reliance, which earlier this year was involved in a fight for control of Sharon Steel Corp., said it has invested $2.9 million to purchase 197,000 shares of San Juan Racing.

Reliance's stock purchases won't upset San Juan Racing's plans to sell its radio stations to Shamrock Communications, a company controlled by the family of the late Walt Disney's brother, Roy, said H. N. Glickstein, chairman of SJR.

In October the Disney group said it was willing to pay $62 million cash and assume $5 million of debts in exchange for the 10 radio stations owned by San Juan Racing. The stations included WUST-AM and WJMD-FM in Washington.

A year ago, the company received an offer to sell out to a group headed by Larry Israel, former president of The Washington Post Co. Those talks ended last February, but San Juan Racing's owners continued to seek a buyer.

The company's board of directors includes several prominent Washington businessman, including Robert Philipson, president of an accounting firm, and lawyers Raymond Dickey and Martin willig.

Glickstein said the formal agreement with Shamrock could be completed within a month, but the sale of the radio chain will require approval of the Federal Communications Commission.

Reliance Group said it paid from $14.50 to $16.525 a share for San Juan Racing stock, which it purchased "for investment." Reliance said it may buy more stock.

The pending Disney deal doesn't include San Juan Racing's original enterprise, the New El Commandantee Race Track in Puerto Rico, or its other real estate holdings, Glickstein said.