While Congress considers the merits of a $50 tax rebate for 1st about everybody, more than 1.5 million persons - many of them poor, sick or disabled are facing an unexpected tax bill of 10 times the proposed rebate because of an admittedly ill-time tax "reform" Congress passed late last year.

The tax reform act cleared in the closing days of the last Congress eliminated the $100 weekly maximum tax exclusion for most people drawing temporary sick or disability pay. Until then, persons who were out with extended illness could exclude up to $5,200 a year (or $100 a week) of their sick or disability pay from their federal taxes. Many states offered the same tax exclusion.

Congress changed the law so that only persons who are medically certified as being permanently and totally disabled could use the tax-exclusion benefit. Congress unwittingly pulled a fast one on the individuals who had been using it by knocking out the exclusion retroactive to Jan. 1, 1976.

That effective date means that the million and a half persons who had, in good faith, counted on using the tax exclusion in computing their 1976 tax bill cannot do it now. It means nearly all of them owe Uncle Sam more money - some as much as $600 to $1,800 - than they thought.

Many of the individuals who had counted on the sick or disability pay tax exclusion are federal workers, disability retires from government or industry or ex-policemen (and women) and firemen injured in line of duty.

Because the federal rules have been changed, many states have also gone along and eliminated the sick and disability tax exclusion for 1976. So the state tax bite for hundreds of thousands of persons will be bigger, too. And the tax-paying deadline is getting closer.

There is a simple way out, if Congress will take it and act quickly. Just change the effective date of that portion of the tax reform act from Jan. 1, 1976 to Jan 1, 1977.

Sen. Robert Dole (R-Kan) and Rep. Robert W. Daniel Jr. (R-Va) have introduced bills to change the date from 1976 to 1977 and save people those big - and very unexpected - tax bills. Dole has picked up important bipartisan support in the Senate and Daniel has more than 100 cosponsors, including most area members of Congress, in the House. Time is the problem.

Backers of the Dole-Daniel plan had originally hoped to tack their bill changing the effective date of the tax exclusion cutoff to the Carter tax reform plan. The House Ways and Means Committee said, for good tactical reasons, that it didn't want the President's important bill cluttered up with amendments that could delay or even kill it. Chairman Al Ullman (D-Ore.) has promised quick action on the Dole-Daniel plan. He hopes to get it through next month.

That will be running it close for the million-plus people who now are scratching around for money to pay a tax bill that resulted from a retroactive legal change. If the Dole-Daniel bill isn't cleared in time, maybe the people hitby the law can use the $50 tax rebate theu may be getting to pay partially the $600 or more in extra taxes they definetly will have to pay.It's something for House members - now on a long recess or working vacation back home - to think about.