The new 5.5 mile segment of Metro subway into Northwest Washington and Montgomery Count open its gates to the public this morning for rush hour commuters.

The extension of the Red Line subway from the Rhode Island Avenue station to Brookland, Fort Totten, Takoma and Silver Spring will begin at 6 a.m. and will continue operations until 8 p.m.

Major changes in the bus routes to the four areas will not be made for another two weeks. Parking for commuters intending to board the subway at Silver Spring will be limited, however, since the 1,100 parking spaces estimated by Metro to be needed will not be available for up to 18 months.

Montgomery County officials are worried that the opening of the Metro line will bring more cars to downtown Silver Spring than there are parking places for them.

"If we had one message it would be that there just is not much parking," said Richard J. Lynch, director of the county's department of transportation. There is a 400-space garage at Bonifant and Dixon, across the street from the Silver Spring Metro station.

But parking meters on the streets of downtown Silver Spring have been rolled back from a 12-hour maximum to a nine-hour maximum to keep all-day commuters out. "That's not what those spaces are for," Lynch said.

Parking will be difficult at two of the three other new stations opening Monday, too. There are no parking spaces at Brookland and only 50 at Takoma - and there's a catch at Takoma.

Parking will not be permitted there until 10 a.m. shutting out the morning rush-hour patron. It's intentional.

At Fort Totten, a 300-space parking lot is available all day.

What the public transit industry has come to call "kiss and ride" spaces are available at all the Metro stations except Brookland. A "kiss and ride" space is one where a driver can wait in a car for someone who is expected on the next train.