U.S. borrowers stymied by lenders that refuse to cut their mortgage principal to market levels should just keep trying, as lenders may have a change of heart, an Obama administration official said on Thursday. A Federal Housing Administration staffer, hosting one of four conference calls to brief brokers on its "short refinance" program this week, confronted a few critics among routine questions about a plan that addresses the massive problem of homeowner equity lost during the housing slump. The FHA is part of the U.S. Department of Housing and Urban Development. The program has been pitched by FHA Commissioner David Stevens as "the single most effective way" to cut principal for homeowners who owe more than their home is worth. With some 11 million loans underwater, the problem is one that academics see as the main hurdle to U.S. economic health, as borrowers feel poorer and have trouble refinancing or moving. The program is controversial for lenders since they must write down at least 10 percent of the mortgage principal and refinance the borrower into an FHA-backed loan.