The San Francisco Board of Supervisors heard nearly four hours of public testimony as hundreds of public health patients, nurses, and advocates urged legislators to stave off huge service cuts by asking voters to approve new taxes. But the supervisors put off a vote that would have scheduled a controversial election for June 2 and also delayed a decision on a number of proposed alternative cuts that are meant to save some health services. The city is facing a $576 million shortfall in the next fiscal year, in addition to the $118 million hole for this fiscal year.