Here is some official advice from the Internal Revenue Service for more than a million taxpayers who have been watching Capitol Hill for signals as to how much they may get back, or owe, Uncle Sam this year.

The problem resulted from the 1976 tax reform act. Among other things, the complicated changes eliminated the maximum $100 a week federal tax exclusion benefit on income from sick or disability pay.

Since the change came late in the year, many individuals who had estimated their 1976 tax bill on the assumption they would not have to pay taxes on those sick or disability benefits got a horrible jolt. It meant that they owed a lot of money when most thought they might break even or even get a refund from Uncle Sam. The individual bite for some of the million-plus individuals involved is as much as $600.

Since almost the first day of this new Congress, two members -- Sen. Robert Dole (R-Kan.) and Rep. Bob Daniel (R-Va.) -- have been working to get the law changed so that the tax break would be retained for 1976 income. Under their bills -- which had bipartisan support -- the sick pay tax would not become effective until Jan. 1, 1977.

Both the Senate and House have been working hard to get the language into a form that will pass before the April 15 tax deadline. The Senate has made it part of President Carter's tax rebate plan, the House is working on it as a separate bill. It has cleared the House Ways and Means Committee and could get full approval of the full House Monday or Tuesday.

Meantime, many of the million-plus individuals who have questions about what to do, have been waiting for a sign from IRS. Here it is, the official IRS guidelines to taxpayers. It tells what to do if you have already paid the tax, or how to ask for an extension if you have not. IRS says:

"The tax reform act of 1976 changed the law regarding exclusion for sick pay proposed legislation seeks to change the effective date of this provision of the law from Jan. 1, 1976 to Jan. 1, 1977. If the legislation is approved and you have already filed your 1976 tax return with sick pay income included in it, you should file an amended tax return (Form 1040 X) in order to reduce your tax liability.

"If you have not already filed your tax return, you, as well as other taxpayers, are entitled to file an application for automatic extension of time on Form 4868 in order to get a 60-day extension. Taxpayers applying for this extension of time should know that they must pay the total tax due under existing law as computed on the extension request Form 4868."

New 20-Year Club: Legislation coming up on Capitol Hill may give a new definition to the term 20-year man heretofore limited to the military.

The proposed bill would guarantee that women (and presumably men) who stay married to a government employee for at least 20 years will get a piece of his (or her) pension, even if they are divorced when the employee dies. The problem now is that many men (and women) shed a mate of long-standing and the new spouse gets all the goodies from the employee's pension.

The bill, which will come before the House Post Office-Civil Service Committee, would guarantee wife (or husband) number 1 with 20 years of marital service part of the pension. They would split the survivor annuity with the wife or husband of the employee at time of death. People who get married several times would, in effect, be providing partial survivor benefits for the first spouse (the 20-year veteran) and the last. But none in between.

The bill, if it makes it through Congress, could do more to cement marital relations in Washington than Jimmy Carter's request to HUD employees to stop living in sin, get married and/or stay married.

If you lunch at one of 31 government cafeterias here, you may be brown-bagging it this fall. Government Services Inc., which supplies the food and servers, says it will terminate service in early October unless it can find a way to run in the black. That sounds like a request for a price increase. GSI made a similar threat in 1975 but decided to carry on.