SEVEN YEARS AND several exhaustive hearings ago, Congress undertook to end one of its sleazier giveaway programs -- the much-abused police and firefighter disability-pension system for the District of Columbia. Not only was it scandalously wasteful and routinely exploited, it was financed in the shakiest of pay-as-you-go-broke ways, as were the pension plans for local judges, teachers and school administrators. But this week, once again, Congress has come up with an important measure to halt the greed and put legitimate pension payments on a sound financial basis.

Only a year ago President Carter killed just such a bill with a pocket veto, having mistaken it for a fat federal spending measure. The delay caused by that blunder has cost taxpayers perhaps as much as $180 million. Now a new, slightly modified measure has been drawn up and reportedly has finally won a nod of approval in the White House. It still centers on the establishment of a fund from which interest payments could be used to help offset existing retirement obligations. The federal government would pay 80 percent of the cost of pensions. The legislation also would abolish the loose disability provisions that have led to the most gross abuses in the past.

Without these changes, the cost of pensions in the next 20 years will equal and then surpass all other spending by the city.That outlandish proposition should be rejected this year by Mr. Carter.