Memo to congressional investigators:

The Civil Service Commission is going to pot. People at the merit system agency are openly breaking the rules and laughing about it. Check this out.

Yesterday the CSC had its annual honors award ceremony. It's an almost sacred occasion devoted to long service and outstanding workers. Yet CSC brass couldn't resist bending another rule for another VIP. It was terrible!

What they did - before hundreds of employees, a congressman, union leaders, veterans cheifs and reporters - was to give a 30-year pin to a man with only 29 years, 6 months and 11 days of service.

The fellow who got the honor was - you guessed it - Chairman Robert E. Hampton. Hampton, a Republican, is leaving the CSC after 15 years, for obvious reasons. President-elect Carter wants to appoint a Democratic chairman.

After the regular CSC employees got their awards, executive director Raymond Jacobson surprised the audience by announcing that he had researched Hampton's federal career and found he had 29 years, 6 months and 11 days of federal and military service. Jacobson said the other two CSC commissioners, Lud Andolsek, a Democrat, and Georgiana H. Sheldon, a Republican agreed to bend the rules and give Hampton a 30-year pin.

You may have a little trouble getting material for prosecution, however. Hampton - despite many lumps from the press, some deserved, some not - was a remarkably popular boss.

Hampton had the misfortune to preside over the CSC at a time when the White House improperly tried - with some success - to put its own stamp on the career bureaucracy. It also was the post-Watergate period of morality when everybody was taking a closer look at things, including real and alleged abuses of the merit system.

(Investigators Note Some of the congressmen who slammed Hampton the hardest on merit system abuses called him before and after hearings to ask about jobs for friends. In the interest of a less complicated probe, you may want to skip all references to that).

If Hampton has been left cynical by the experience of being on the hit list of both the Nixon White House and the Democratic Congress, he looked amazingly calm and happy yesterday. Maybe it was the three standing ovations he got from longtime coworkers, who really didn't have to be all that enthusiastic about a boss who won't be the boss much longer.

His public record will be debated for a long time by people interested in the merit system during the Kennedy through Ford years. But his apparent popularity with the staff is rather touching in this day and age when people are trying to cultivate new leaders and disavow the old as quickly and loudly as possible.

Maybe the best tribute of all comes from a veteran CSC aide who is known to mistrust - if no dislike - anybody above Grade 15. He said Hampton would be a "very tough act to follow." Not a bad way to leave office. But about that 30-year pin . . .

What lame Duck? American Postal Workers union chief Francis S. Filbey says he likes his work and will decide - no matter what this column says - when he will retire.

Filbey was upset with the Jan. 13 account here that quoted him as saying his union is top-heavy with 49 national officers (with a $1.6 million payroll). That part is all right, Filbey says. But he takes issue with our reference to him as a lame duck.

Describing him as a lame duck, he feels, implies that he withheld his blast at the union hierarchy until he had no further political ambitions. Not so, says Filbey. As of this moment, he says, he plans to be a candidate for re-election in 1978, so remove that term "lame duck", from the Jan. 13 story.