After months of negotiations, one strike and the threat of another, and intervention from the governor, Johns Hopkins Hospital and 2,000 service workers reached a tentative labor agreement early Tuesday that some said could become an "important benchmark" for the health care industry. The deal, which is to be submitted to the workers for a vote, came after seven hours of negotiations that ended at 2 a.m. It would affect housekeepers, cooks, janitors, surgical technicians and others. Officials with 1199 SEIU United Healthcare Workers East said the agreement was prompted by an offer of raises for workers with at least 15 years of experience.