BROWNSVILLE, Texas (AP) _ A transit-system parts clerk was found innocent Wednesday of forging $200 in checks for a department Christmas party in 1985, dealing another blow to a Texas Rangers investigation of City Hall.

The acquittal of Cayetano Ovallo followed the dismissal on Tuesday of a theft charge against Mayor Emilio Hernandez before testimony could begin at his trial. He was accused of using city money for campaign brochures in 1983.

''I can't believe that the Texas Rangers were involved in this fiasco, because this has probably been the most one-sided investigation that anybody could have done,'' said Albert Villegas, Ovalle's attorney.

Texas Ranger Rudy Rodriguez, who coordinated the graft investigation begun in November, did not return repeated calls to his office for comment Wednesday.

Leo Gossett, state Department of Public Safety director, said, ''No one has brought to my attention any information, specific or otherwise, which would indicate that this Ranger investigation was not fair and objective.''

A grand jury had returned indictments accusing six public officials of offenses including bribery, gift solicitation, witness tampering, official misconduct and forgery.

Later it was discovered the grand jury foreman had a criminal record, and the indictments were dismissed. A new grand jury indicted only the mayor, Ovalle and another parts clerk and a city commissioner.

Those charges eventually were dismissed against all but Ovalle and the mayor.

Only two cases remain, both against Hernandez, who faces trial on charges of aggravated perjury and soliciting a bribe from a company bidding on a garbage contract.

Ovalle was accused of forging endorsements on two $100 checks. A prosecution witness changed his story more than once in the case.