Opponents of the Los Angeles Metro Rail project announced they will attempt to qualify a county ballot initiative aimed at blocking the use of special tax dollars to finance the initial 4.4 miles of the subway line. Members of the Alliance for Rapid Transit said they will launch a petition drive to halt the use of funds to build the first leg from downtown's Union Station to MacArthur Park. The money comes from Proposition A, the half-cent sales transit tax initiative passed by county voters in 1980. But representatives of the anti-Metro Rail group claimed the subway would prove too costly, would not relieve traffic congestion and was not what voters had in mind. Alliance members said they hope to collect more than 200,000 signatures to qualify the measure for the ballot. County supervisors also would have to approve placing the measure on the ballot.