IN THE MISGUIDED belief that he was rescuing the country from another fat federal spending bill last November, President Carter pocket-vetoed one of the most important legislative achievements of the last Congress in behalf of the District of Columbia. As every supporter of the measure could have told him, the idea was not to waste money but to save it, by the bundle: the bill would have ended the enormously expensive racket that has been passing for decades as a police and firefighter disability -- pension system in this city. It also would have stabilized the shaky financing of these pensions, as well as those for local judges, teachers and school administrators. But it died at Camp David -- and the bills keep coming in.

In Congress, where seven years of hearings and careful consideration have gone into this legislation, members are trying one more time to halt this underhanded giveaway program before too many more millions of dollars are wasted. Rep. Stewart B. Mckinney, ranking minority member on the House District Committee, says the delay caused by last year's veto already has cost taxpayers from $150 million to $180 million. Now, in a significant attempt at compromise, leaders in the House and Senate have shaved the share of federal financing that would be involved in reshaping the pension system and curbing abuses.

The compromise was suggested by District Committee Chairman Ronald V. Dellums, who, along with his Senate counterpart, Thomas F. Eagleton, and Mr. McKinney, has worked over the years for pension changes. Mr. Dellums points out that unless the bill is passed, the cost of pensions in 20 years will equal and then surpass all other spending by the city. It isn't as if this system were a local creation, either -- this was begun by Congress a good 50 years ago, and the error has been compounding at a frightening rate ever since.

In addition to clamping down on disability-pension abuses, the solution being proposed is for the city to start setting aside a fund for the next 20 years so that a large part of future retirement benefits could be paid from interest earned from the fund, rather than on a pay-as-you-go-broke system. This time, President Carter should recognize a sound financial proposal and join Congress in its enactment.