But the Congressional Budget Office reported this year that a $500,000 ceiling on the mortgage principal for which interest can be deducted would raise $48 billion over 10 years.

Monthly housing expenses, he said, include mortgage principal and interest payments, property taxes and hazard insurance.

It is usually computed monthly by dividing the monthly payment by the mortgage principal.

In addition, the normal requirement that payments on mortgage principal and interest not exceed 28 percent of gross household income is eased to 33 percent.

Still, they managed to reduce their monthly payment for mortgage principal and interest by $127, to $1,082.

That discounted bond would pay the mortgage principal on maturity, with the Graham company making only the monthly interest payments.

Negative amortization mortgages, in which part of the interest is piled on to the mortgage principal, have also become rare.

But a problem arises, Mr. Shine said, when the banker merely adds the cost of the points to the mortgage principal.

Those 26 installments provide one extra full payment each year, which is used entirely to reduce the mortgage principal.

Critics, however, say that any homeowner tempted to spend money on a biweekly program would be wiser to put it directly toward reducing mortgage principal.