One of the hottest, most persistent rumors making the rounds in government today has it that President Reagan is ready to furlough most of the bureaucracy for eight to 10 days this month. Congressional offices and newspapers have been swamped with frantic calls and letters from Hyattsville to Honolulu from people asking about the rumor -- that is false -- or those who got it from a friend of their brother-in-law who heard it from a usually reliable barber.

The White House and the Office of Personnel Management say no government-wide furlough is being planned or is in the works. Office of Personnel Management Director Donald Devine says he has heard the rumor, mostly from congressional staffers calling or writing because nervous federal constituents are wondering whether to buy Christmas presents or give each other IOUs this year.

Under federal rules, agencies cannot furlough employes -- except in emergency conditions -- without giving workers 30 days' notice. Some Navy and Defense units outside of Washington are planning regular Christmas-to-New Year's shutdowns. But these are routine, and workers are allowed to take paid leave if they have it, and are not being furloughed. The Bureau of Engraving and Printing will have a shutdown, but that was announced some time back.

Department of Education officials say they have been plagued with the false rumor -- growing out of a Dallas conference -- that the department's employes are to be furloughed Dec. 15. Not true, they say.