Military retirees who take civilian federal jobs after Oct. 1 would have to give up their military pension checks under legislation the House will consider Friday.

The bill would eliminate the practice of "double-dipping" whereby military retirees hired by Uncle Sam as civilians get a monthly pension check for military service and another check every two weeks for their civilian government job.

The legislation would not affect the status of the 141,000 military retirees who now work for the federal government. But it should be the legislative foot in the door that might lead to similar pension cutoffs or cuts for them.

In a "normal" year, about 68,000 people retire from the military. Between 12 and 15 per cent of them, according to congressional sources, take civilian federal jobs. Between 1972 and 1976, an estimated 20 per cent of all military personnel who retired entered government.

According to Pentagon figures military pensions now cost about $9.6 billion a year. Of that , amount, it is estimatedt $9.6 billion a year. Of that, amount, it is estimatedlion for former service, in addition to whatever they make from their civilian federal jobs.

Retired regular officers may keep only a portion of their military pensions (the first $4,000. plus half the remainder). Retired reserve officers and all former enlisted personnel, who make up the bulk of the government's military retiree population, get to keep all their military pension plus their full civilian salaries.

The dual compensation cutoff is a rider to the Defense appropriations bill that goes before the House Friday. Debate will take a long time on the money package and it could be Monday or even later next week before a final vote. The Senate appropriations Committee has approved a similar dual compensation cutoff, also with an Oct. 1 effective date.

House Appropriations Committee Chairman George H. Mohon (D-Tex.) is pushing for the dual compensation cutoff. His clout - as one of the most powerful members of Congress - gives the controversial rider a good chance of passage.

The White House has quietly told key President would sign the measure, although on the matter. Earlier, Carter ran afoul of the military and veterans' lobby when he took some verbal pot-shots at "double-pippers," and now wants to let the intiative against them come from Congress.

Sign In, Sign Out: U.S. Postal Service headquarters employees are being required to sign in if they arrive for work after normal starting times, and to sign out if they leave before normal quitting time. To be sure the employee is signing the right name, official U.S. Postal Service identification must be shown to security guards.

USPS official says this is part of the ongoing security program, and also because of the "continued unauthorized late arrival and early departure of some postal employees, as well as extended periods of absence from work locations during the day."

Public Employees Department: The AFL-CIO coalition of federal, postal and public unions has elected American Federation of Government Employees President Kenneth T. Blaylock as treasurer. Blaylock succeeds the late Francis S. Filbey.

D.C. Retirees: Pensions of retired D.C. teachers and benefits for the survivors of teachers, police officers and firefighters may be going up in September. Exact amount of the increase depends on the Consumer Price Index, but it now appears that the amount will run about 3.6 per cent.

Teachers eligible to retire will want to keep an eye on the pension-boost possibility. Personnel Director Goerge R. Harrod says teachers who retire before Sept. 1 would receive the increase "while those who retire later would have to wait until the next time an increase is granted." That would be April, 1978.