Salaries of federal workers -- now tied to the going rate for similar jobs in the private sector -- would be based on a supply-demand system under a plan being considered by the Office of Personnel Management.

If OPM adopts the idea (one of a number of salary overhaul plans to be considered) and Congress approves it, government workers could get different pay raises based on where they are located and what they do.

Under the present system, federal pay is supposed to be adjusted each October based on data collected by the Bureau of Labor Statistics showing how federal pay compares to pay scales in private industry. One idea getting serious consideration at OPM is to discard pay surveys. Instead, the government would base decisions to raise, freeze or lower pay on comparisons of the so-called real quit rate -- the number of people who voluntarily leave their jobs -- in government with voluntary turnover in the private sector.

The average salary of government workers in the Washington area is $30,784 a year, while the median (middle) federal salary here is $27,252. Outside of Washington, the average federal salary is $25,247, while the median civil service salary is $22,336.

Some OPM officials believe that using the quit rate to determine how well, or poorly, the government is paying people is the best way to know when to give raises.

Although the current system of matching salary levels in the private sector is supposed to be automatic, the past four presidents have lowered the recommended amounts. President Reagan has not only lowered the amount recommended by government pay experts but has also delayed the effective date of the raises until January.

This past summer, for example, the pay data showed that federal workers were due an 18 percent raise in October to bring pay for similar jobs up to industry levels. Reagan reduced that to a 3 1/2 percent, effective next month.

Last year the pay data showed federal pay more than 20 percent behind industry. Reagan nevertheless set the raise at 3 1/2 percent effective last January. Congress later voted an additional 1/2 percent raise for employes, making the 1984 increase 4 percent.

A compensation report being prepared for OPM Director Donald Devine says that the voluntary quit rate in government is 3.8 percent. That, the study says, is three to four times lower than the turnover rate in industry.

Using that data, OPM officials say the government can cut federal salaries 5 percent next year (a proposal that will be part of Reagan's budget next month) without serious loss of personnel. Congress would have to okay the pay cut.

Many federal workers -- including top statisticians -- question the OPM conclusions and data.

If the government used quit-rate data to determine raises for its employes, workers in areas where Uncle Sam was having a hard time hiring and keeping employes could get raises. Civil servants in areas or occupations where the industry quit rate was lower would get smaller increases.

Christmas Eve Policy: Although Monday Dec. 24, is a workday, federal supervisors are being encouraged to let employes go home early. This is the official word from OPM Director Devine:

"In order to accommodate the family gatherings traditional on the evening before Christmas, the heads of executive departments and agencies are encouraged to grant liberal leave for that day. For employes who choose not to charge leave, supervisors may grant a few hours of leave without charge for a portion of the workday this Christmas Eve, Dec. 24, 1984."