It was a startling declaration: here was Bill Hansbarger, a zoning attorney whose legal assault on Fairfax County's zoning laws 20 years ago opened up the farthest corners of the county to automobile-driving suburbanites, saying, "The day of the solo commuter is over."

Admittedly, Hansbarger arrived at his heretical conclusion largely out of self-interest. One of his clients, in a strenuous effort to win county and citizen approval for a large corporate office on badly congested Route 50 at the Capital Beltway, has offered an elaborate transportation package aimed at discouraging solo commuting.

Yet I think Hansbarger's conclusion gets to the heart of some remarkably changing attitudes about commuter transportation, especially among surburbia's powerful car constituency. (Self-interest, more than altruism, prompted these changes, but if it is self-interest that gets solo commuters out of their cars, is that bad?)

Some gleanings from this area:

The number of cars crossing the Key, Roosevelt, Memorial and 14th Street bridges has decreased from about 74,000 to about 67,000 in a year, while Metrorail's Blue Line traffic across the Potomac rose from 15,582 to 23,495.

In the distant Fairfax suburbs, many residents, either tired of coping with stop-and-start congestion three hours a day or trying to avoid the ever-increasing financial burden of a second car, are clamoring for Metrobus service.

In Montgomery County, the Planning Board and County Council are considering proposals that would tailor growth in heavily traveled corridors to the acceptable "thresholds" of traffic on major roads.

To ease congestion in Silver Spring, where commuter-hour car occupancy is a pathetically low 1.1 to 1.2 persons per vehicle among the 17,000 workers who drive, the county is trying to establish a ride-sharing program that would give car-poolers the choicest locations in public garages.

In Prince William County, 75 vans are ferrying former solo commuters to Washington, and the county government has received state aid to augment the largely volunteer pooling effort.

Elsewhere in the country, there are even more impressive indications that solo commuting is no longer an article of faith. For example, in sprawling, car-conscious Houston, Conoco Corporation has put 38 percent to 30 percent in car pools. With only half as many employees to match up, Aramco has done as well with van pools.

Van pooling can save a lot of money for commuters: a 20-mile round trip can cost only a little more than a dollar if vans are company-subsidized. The potential for saving oil through van pooling is enormous. A well-organized program at a company or job center, the statistics show, can reduce commuter trips by 40 percent. Even a 20 percent reduction nationwide would save up to 500,000 barrels of oil a day -- or a third of what an expensive synfuels program promises, no sooner than 1995.

But to cut commuter traffic by even the conservative figure of 20 percent will require private industry and local government -- together -- to do what is being done in an isolated way around the country.

Traffic control works, the case studies show, when employers set specific objectives in traffic reduction and carry them out as determinedly as if they were sales goals. Both industry and government will have to face up to charging for parking where it has been traditionally free. Already, free parking is coming to an end at all federal installations in the metropolitan area.

Just as it has been insisting on traffic controls at the project planned by Hansbarger's client, local government will have to do the same elsewhere when development is proposed.

None of these efforts to reduce traffic needs to interfere with the great American love-affair with the automobile. The affair can go on -- but, please, not during business hours.