This promises to be a miserable weekend for more than 1 1/2 million taxpayers - many of them sick, old or financially hard up - who must come up with an extra $200 to $1,900 to pay their 1976 taxes.

What happened - or rather what didn't happen - was that the Senate in its rush to go home for 10 days left town Thursday night without acting on a bill to clarify a clause in the tax reform act. President Carter didn't help much by sending word that if they remained in session he would probably veto the tax-saving bill the Senate had cleared earlier by an 84-to-0 vote.

Congress - led by Sen. Robert Dole (R-Kan.) and Rep. Bob Daniel (R-Va.) - has tried very hard since January to make up for a mistake it made last year. Late in 1976, it passed the comples tax reform act. One section of it wiped out the $100 a week maximum sick and disability pay tax exclusion for more than 1 1/2 million people.

The problem was that by the time Congress got around to eliminating the tax break for the year 1976, the year 1976 was already nine months gone. That meant that millions of taxpayers who had been planning to take the sick and disability tax breaks for that tax year suddenly learned it was no longer possible. In dollars and cents, it meant that many of the people - a lot of them retired or disabled federal workers - unexpectedly owed Uncle Sam hundreds or thousands of dollars more than they expected they would.

Congress admitted that the Jan. 1, 1976, date for cutting off the tax benefit was a mistake. Clearly Congress had intended for the tougher new standard to begin Jan. 1, 1977.

Dole and Daniel - with backing from the Democratic leadership - got an early start on the bills to change the effective date of the tax benefit cutoff from January, 1976, to January of this year. Everybody figured it would be a close call, the way Congress does things. But there was genuine hope the issue could be straightened out by the APril 15 tax-filing deadline.

Many individuals who hoped to benefit from the sick and disability pay exclusion held off filing their income taxes, believing the Congress would correct its oversight.

The House approved the Daniel bill overwhelmingly and the Senate approved the Dole bill without dissent. But amendments were tacked onto the Senate bill (unrelated to the tax change) and the House refused to accept them. The House went into its Easter recess Wednesday. That meant that the Senate had to clear a "clean" version of the tax package, the version acceptable to the House, before it quits on Thursday.

The Senate ran into trouble. And then came word from the White House that President Carter might veto the Dole-Daniel plan anyway since it would reduce estimated 1976 tax revenues by about $300 million. The drive fell apart and the Senate quit.

Dole promises to push his bill again when the Senate reuturns (April 17) and to tack it onto a piece of legislation the President cannot veto. But that will take time, and April 15 is the tax-filing deadline.

Individuals who received sick or disability payments in 1976 now have two options:

They can pay their taxes by the April 15 deadline and hope for a refund later (by filing an amended return) when and if Congress straightens the matter out, and the President signs it into law.

They can ask for an automatic extension (Form 4868) - many will since they don't have the money to pay the extra taxes - and hope the law is changed before their 60-day extension expires.