Tens of thousands of federal employes who drive to work in Washington each day have been given an additional month of free-and cut-rate parking privileges before the Carter administration's pay-to-park policy becomes effective.

In announcing final guidelines for the program, the Office of Management and Budget said that the program would begin Nov. 1 rather than Oct. 1 as originally planned. The delay was necessary, OMB said, to give agency administrators sufficient time to establish rate schedules and fee collection programs.

Beginning Nov. 1, about 350,000 U.S. employees nationwide -- including more than 75,000 in the Washington metropolitan area -- will have to pay a parking fee equivalent to half the prevailing commercial rate in the neighborhoods in which they work. Starting Oct. 1, 1981, the fee for employees will be increased to the full commercial rate.

In setting the final guidelines, OMB allowed agency directors to grant a number of exceptions. Those include persons who work weekends, early or late night shifts and handicapped persons who operate specially equipped vehicles. Persons participating in van pools will be allowed to continue parking free or at reduced rates until Oct. 1, 1981.

Most of the exemptions permitted are in line with the stated purpose of the program -- to encourage car and van pooling and increased use of public transportation.

Workers on flexitime and overtime will not be exempted.

Exceptions are permitted for patients, visitors and patrons at such facilities as hospitals, commissaries, post theaters and chapels.

The major group exempted from the plan will be persons in those areas where commercial rates are less than $10 per month. This is likely to be the case at most military installations, OMB officials said yesterday.

In the Washington area, where commercial parking rates range from $20 to $80 per month, few exceptions are expected.

For example, the prevailing commercial rate around the Pentagon is estimated to be about $15 to $20 a month. It is about $75 a month in the area around the White House and $20 to $25 near the Parklawn facility in Rockville, according to federal officials.

The plan will not cover postal workers, judges, members of Congress or their employes. Also exempt are two-wheeled vehicles. Van pools will be exempted only until Oct 1, 1981, when they will begin paying parking fees as well.

Individual agencies will be allowed to make final determinations on the granting of additional exemptions.