President Obama is going to unveil a real mortgage relief plan, about three years after he should have.

It’s got some very good elements, but it is crying out for some income limits.

Here are the major elements of the plan, according to the Washington Post:

• Banks and other lenders would have to reduce the payments to no more than 31 percent of a borrower’s income, which would typically be the amount of unemployment insurance, for three to six months. In some cases, administration officials said, a lender could allow a borrower to skip payments altogether.
• The government will provide financial incentives to lenders that cut the balance of a borrower’s mortgage. Banks and other lenders will be asked to reduce the principal owed on a loan if the amount is 15 percent more than their home is worth. The reduced amount would be set aside and forgiven by the lender over three years, as long as the homeowner remained current on the loan.
• The government will double the amount it pays to lenders that help modify second mortgages, such as piggyback loans, which enabled home buyers to put little or no money down, and home equity lines of credit.
• More incentives will be paid to those lenders that find a way to avoid foreclosing on delinquent borrowers even if they can’t qualify for mortgage relief. For example, the administration is scheduled to launch a program next month encouraging lenders to have borrowers sell their homes for less than the mortgage balance in what is known as a short sale.
• The FHA will offer incentives to lenders that reduce the amount borrowers owe on their primary mortgages by at least 10 percent.

All of those are much-needed measures, but should be limited. There is a fundamental difference between a family of four living on in a 1,500-square-foot house and a twosome living in a 3,500-square-foot monstrosity. Even if layoffs equalize the two households incomes, the former should simply be given more consideration. The couple in the bigger house has more options — like downsizing.

This proposed measure will provide a little relief, but probably less than will be hyped. A six-month mortgage grace period, in the form of lower payments, may really benefit those who can find a job within six months, but will only delay the inevitable for those who can’t and will cost taxpayers a tidy sum even for those not ultimately helped.

It also would be nice for the government to include a “stupid choices” factor that would disqualify homeowners who can’t make their mortgage payments because they made stupid choices — fancy car debt over a savings account, for example, or a $600,000 house on a $100,000 income.

It is, alas, unlikely that the federal government, which often moves with the grace of a large bulldozer, will make those fine distinctions. And this bailout will cause resentment, too.