Employees at Boston-based Beth Israel Deaconess Medical Center are mostly praising the chief executive's proposals for slashing the number of potential layoffs from more than 600 to about 150 through a combination of wage freezes, salary cuts in high administrative jobs, and benefit reductions. The chief executive, Paul Levy, has held meetings with employees to find ways to spare the lowest-wage earners from the budget ax he needs to wield as revenues fall short by $20 million.