As the number of Americans who owe more on their homes than they are worth grows — 8.8 million homeowners, or 10.3 percent — the Bush administration and Congress are considering costly ways to help. The percentage of homeowners with negative equity has doubled in just a year. Bank of America has floated a proposal similar to one offered by Senator Christopher Dodd, Democrat of Connecticut and chairman of the Senate Banking Committee. The proposal is to create a new federal agency that would buy delinquent mortgages at a deep discount and replace them with fixed-rate federally guaranteed loans. Meanwhile, the mortgage industry’s leaders say the Federal Housing Administration’s new insurance program, FHA Secure, is too restrictive.