The U.S. economic recession is forcing many Massachusetts hospitals to reconsider ambitious expansion projects, put major purchases on hold, and eliminate jobs as revenues and investments shrink. Tight credit markets have made it difficult to borrow money, investment income used to supplement medical revenues has withered or turned to losses, and patients are putting off elective surgery because of high deductibles and copayments, hospital officials say. The healthcare cutbacks could produce a ripple effect extending to nursing agencies, equipment suppliers, and other businesses that support hospitals.