Opposition to a rule that would ban the use of the diuretic Lasix in Grade I stakes events in Maryland is mounting. The rule was passed by a 4-to-1 margin at Thursday's meeting of the State Racing Commission in Baltimore.

Charles (Chick) Lang, general manager of Pimlico, said yesterday, "This doesn't make sense. Other jurisdictions that use Lasix will be getting many of the better horses who use that medication. Since only New York and Arkansas bar the use of the diuretic, you can see that we can lose out in attracting many fine horses for our Preakness and Washington, D.C. International. Of course, we intend looking into the possibility of an appeal."

The rule change must be approved by a panel of delegates and senators in the General Assembly. Although those committees usually uphold commission decisions, this one may face opposition, according to Jack Cooper, an assistant state attorney and commission adviser.

Commissioner Joe Hickey, the sponsor of the rule, said, "There are so many races run in which Lasix will be allowed in Maryland. We felt that the two showcase events (the only ones affected) should be run free of any drugs." Hickey was joined in his vote by commissioners Ordell Braase, Dr. Roger Scullin and chairman E. William Furey. Ernest Colvin was the lone dissenter.

Strong opposition to the new rule also has come from Ed O'Brien, president of the Horsemen's Benevolent and Protective Association's Maryland Division.