Boston-based Beth Israel Deaconess Medical Center will lay off 140 or fewer employees, using a combination of delayed raises, a temporary reduction in benefits, and donations from department heads to avoid wider job losses. Paul Levy, the hospital's chief executive, revealed the decision in an e-mail message to staff that he posted on his blog. The move follows weeks of meetings and online discussions seeking ways to preserve many of the 600 jobs initially endangered by a $20 million budget shortfall.