Dear Dr. Gridlock:

Several years ago there were 450 parking spaces under the Air and Space Museum. Then there were none! At the stroke of a pen, some lunatic decided that this, THIS mind you, of all the places in the Washington area, was a political terrorist target! Not the Capitol, not the Washington Monument -- a parking garage. I want it back! S. RICHARD BAYLUS Falls Church

You won't get it back any time soon, Mr. Baylus.

The Smithsonian did close the 496-space underground parking garage in mid-1986 because of a worldwide increase in terrorism at that time and concern that terrorists might strike a high-profile target. There was no specific threat directed at the Smithsonian, but its Board of Regents nevertheless decided to close the underground garages at the National Air and Space Museum and those under the Natural History and American History museums.

The threat of terrorism has subsided, according to Smithsonian spokeswoman Madeleine Jacobs, but the garages are not going to be reopened. Instead, they are being used to house construction equipment for long-term remodeling projects and to provide parking for senior Smithsonian employees.

Jacobs said that the three museums that had public underground garages receive hundreds of thousands of visitors each weekend (each receives 6 million to 8 million visitors a year) and that the loss of 800 parking spaces is not significant weighed against that amount of patronage.

She suggests visitors take Metro, or park in the free and metered curbside spots along the Mall, or in any of the several commercial parking garages in the area (the Smithsonian will provide directions if you call 202-357-1300).

The loss of those garages cost the Smithsonian hundreds of thousands of dollars in revenue, Jacobs said, but to open the spots not taken up by construction would not be economically sound.

Another of life's imperfections, perhaps, Mr. Baylus. But now that the employees have moved into the parking garages, you can imagine it is not going to be easy to dislodge them. You might want to board the Metro Orange Line in Falls Church, take it to the L'Enfant Plaza station (Maryland Avenue exit) and walk one block to the Air and Space Museum. That may not be as convenient when you are escorting lots of visitors with tourist spots to visit, but it may be the best available choice.

Linking Outer Metro Stations

Dear Dr. Gridlock:

Most large subway systems throughout the world have "circle lines" linking outer stations with each other. If the Washington Metro had such a line, riders could get from the Shady Grove to Silver Spring stations in one short ride with no intervening stops, instead of the 23 stations through downtown that this ride currently requires.

That same rider could get all the way from Shady Grove to Huntington with only one stop (in Vienna).

A circle line would require no new stations, only the construction of above-ground lines between the existing stations. Although obtaining rights-of-way and modifying the existing stations might cost a bit, it would surely be less than building a new line from scratch.

With so many commuters going from suburb-to-suburb these days, I think such a line should be seriously considered. CRAIG COX Alexandria

Metro spokeswoman Beverly Silverberg says: "This is an appealing thought. It's not a new thought, or unique; it would require a great deal of planning and funding."

Some thought has been given to running Metrorail lines around the Capital Beltway. Although new stations and parking facilities would have to be built, such a plan might be cheaper than connecting the outermost Metro stations, because right of way along the Beltway is already in the public domain.

Much of the area around each of the outermost stations is heavily developed, and acquiring right of way might be prohibitively expensive, even if substantial funds were available.

But, as we know, there is not enough money available to finish the 103.5-mile Metrorail system as originally proposed, and that is Metro's first priority, before any such ambitious extensions. Right now, what you suggest is just "a glint in a planner's eye," Silverberg says.

It's something worth thinking about though, Mr. Cox, particularly with ever-expanding gridlock. The $2 billion proposed (but not approved or financed) Washington Bypass, the extension of Metro, the expansion of railroad commuting or the evolution of a network of bicycle paths, or some combination of these things, may be necessary if people here are going to be able to move in the next century.

Changing Car Pool Minimums

Dear Dr. Gridlock:

In your Nov. 9 column, regarding a suggestion to change Virginia's I-66 from HOV-3 to HOV-2, you quoted state highway officials as saying the road is too crowded to lower the express lane minimums. They also said that no study has been done, and none is planned because it is too expensive.

Many Metrorail riders, including myself, pass the time in the I-66 median by counting inbound cars, dividing them between car pools and HOV-lane violators. Almost every day there are more violators. In fact, if it weren't for the violators, the road would almost be deserted.

HOV-3 on I-66 is a failure. Just ask the Orange Line riders who watch this travesty every day. We don't need an expensive study and we shouldn't have to wait to get action where it is so obviously and desperately needed. JONATHAN A. TAYLOR Burke

Okay, state officials, how about a study? If Mr. Taylor is right, there seems little reason not to switch to HOV-2. That, along with more enforcement, should boost car pooling.

Dr. Gridlock appears in Metro 2 each Friday to explore what makes it difficult to get around on roads, from misleading signs to parking problems to chronic bottlenecks. We'll try to find out why bad situations exist and what is being done about them. You can suggest topics by writing (please don't phone) to DR. GRIDLOCK, The Washington Post, 1150 15th St. NW, Washington, D.C. 20071. Please include your full name, address and day and evening phone numbers.