Negotiators for the Southern California Rapid Transit District and the union representing about 1,700 mechanics reached tentative agreement on a new contract. The provisions of the agreement with the Amalgamated Transit Union are confidential until it is ratified by the membership and the RTD board of directors, said RTD spokesman Jim Smart. The RTD is also negotiating with the Brotherhood of Railway, Airline and Steamship Clerks, which represents clerical workers, and the United Transportation Union, which represents about 5,000 drivers. The contract with the drivers union expired in February, but a Superior Court judge issued an injunction forbiding the union to strike during a 60-day "cooling-off" period. The order expires at midnight April 21, when the contract with the clerks union expires. The bus system has had five strikes in the last 12 years.