This isn't the week to use the check-is-in-the-mail routine on folks at the Internal Revenue Service or Labor Department -- whose checks are really still in the mail!

Upward of 8,000 workers in the two agencies didn't get semimonthly paychecks that were supposed to be delivered this week. Salary payments that are electronically transferred to the banks of employes weren't affected by the snafu.

IRS officials said makeup checks were finally given to employes yesterday. Labor Department officials said they would try to make sure everybody who missed a check gets one today.

What happened to the original checks is unclear, except that most of the 2,554 home-bound checks for IRS workers here, in Maryland, Virginia and West Virginia didn't make it. Checks due many of the Labor Department's more than 6,000 employes east of the Mississippi also failed to show.

Agency officials say the paychecks were picked up as usual by the Postal Service from the main Treasury building next to the White House. After that, things get a little fuzzy.

A Postal Service spokeswoman said the checks were carried to the main city post office for distribution. But, she said, "We just pick up bags . . . . and we don't know how many checks are in them." She added that this sort of thing happened at least once before, and it turned out the Treasury Department hadn't printed checks for all employes. Early Retirement Plan

I panicked lots of sharp-eyed readers yesterday by dropping a line from the column outlining provisions of the early retirement bill introduced by Sens. William V. Roth Jr. (R-Del.) and Ted Stevens (R-Alaska). The bill would allow thousands of employes to take early-outs between July and December.

Employes could retire at any age after 25 years' service; at age 50 after 20 years' service; at age 55 after 15 years' service or at age 57 after five years' service. I left out the 50-20 part, causing understandable heartburn for many 50-years-olds who are watching the progress of the bill.

Hearings haven't been scheduled on the Roth-Stevens bill, but there is considerable support for it, especially among federal workers. Overseas Contracting

Agency for International Development has videotaped a three-part course on procurement and overseas planning techniques for its staff. Project manager Michael Marlow set up the sessions, which feature panels of AID experts who tell what they do, and how and why they do it. The idea is to save on training costs and provide uniform how-to guidelines to employes here and around the world. Crystal Ball Time

The fate of the federal work force is the subject of today's meeting of the Congressional Clearing House for the Future. Reps. Mary Rose Oakar (D-Ohio) and Frank Wolf (R-Va.) will host the session at the Rayburn House Office Building. For information, call 226-3437. Government Drivers Insurance

Civilian and military personnel who drive cars owned or leased by the government can now buy liability insurance protection from Government Employees Insurance Corp. Feds can be held financially responsible for accidents that often aren't covered by their personal insurance. GEICO is offering the coverage for as little as $12 a year. For information, call (800) 841-3000.