The GOP must have been using a well-worn credit card when it ordered up an end to the “marriage penalty” in the federal income tax. Now that the bill has come due, House Republicans figure all they can afford in the minimum payment with a promise to do more later.

The reasons for the marriage penalty vary with income, but generally it is caused by progressivity in the tax code — people who make more pay a higher rate. The Congressional Budget Office reports that more than 21 million married couples pay an average of $1,400 a year more in taxes than they would in total if single. Conservatives in particular have identified the penalty as anti-family, arguing that it discourages people from getting married, and perhaps it does.

What they do not discuss with the same fervor, however, is the “marriage bonus,” which, at an average of $1,300 annually, comes to married couples whose two incomes are widely different. House members know about the bonus, of course, and when they wow the hometown crowd with their determination to smoke out the anti-family conspiracy within the IRS, they know there is nothing of the sort. They know, too, that the people receiving the bonus are just one group among many that could lose out if the marriage penalty were eliminated and that don’t mind telling Congress, quietly, that marriage isn’t all it’s cracked up to be.

The simple answer for the House is not to allow any losers — remove the penalty and let the revenue loss be absorbed by the surplus. Simple, but expensive. Married couples pay about three-fourths of all income tax, so when they get a break it costs plenty, nearly $42 billion a year in this case. The House already is operating under the fiction that it will stay within tough budget caps set a couple of years ago and is saddled with the recognition that it cannot afford the GOP’s proposed $800 billion tax cut over the next decade.

On Tuesday, House Republicans, feeling pressure from moderates in their own party and from Democrats, tentatively offered to stop trying to kill the marriage penalty but just rough it up a bit with a reduction worth a piddling $240 per couple. Conservative groups are not taking it well, although they knew when the GOP pledge was made that it was fiscally unlikely, just as it has been unlikely in each of the five years the GOP has pledged to remove it.

The forthright thing for members of Congress to do is meet with constituents sometime during the August recess and tell them plainly that there’s a long line of groups looking for tax breaks, that this one turned out to be too big to handle and that, chances are, each taxpayer is both a winner and loser a dozen different ways each time he or she files a return. Congress can continue to whittle away at the penalty but don’t expect it to disappear this year.

Then it should cut up its credit card and promise never to make a pledge with one again.