Ronald F. Johnson lives in Centreville. Each morning he drives to his job in Washington by taking Route 66 to the Beltway and then swinging over to Route 50.

"Several mornings each week," he complains, "policemen are stationed at various intersections pulling cars over for traveling in the bus lane, which runs the greater part of the distance between the Beltway and Fort Myer. It took me approximately 20 minutes to travel this distance this morning. My wife counted the buses in the bus lane and found that there were two, neither full.

"Traffic usually moves quite well until I reach Seven Corners, and then it comes to a crawl, all because some idiot decided that the righthand lane should be used solely for buses. Of course many people ignore the law and travel in the lane anyway, and some get caught. With all the crime and problems that require the presence of a policeman, isn't it absolutely ridiculous to have several of them, sometimes as many as five, engaged in this meaningless task? Traffic would move better without their presence."

Ron, nothing I am about to say in response to your letter will make sense to you unless you take my word for this statement: No major urban area can ever feel sure it is building enough roadways and bridges to serve traffic volume adequately one decade later.

We can build enough highway and bridge lanes to take care of the needs that exist when construction begins. But we can't provide enough for the future because the instant more carrying capacity comes into existence, more automobiles appear as if by magic. Residents of the area buy more cars and drive more miles per car.

We're forever looking forward to the relief we'll get when construction projects are completed. But soon after each new facility goes into service, it also becomes a bottleneck that needs relief.

Remember when Shirley Highway was going to end all our problems? The Whitehurst Freeway? The Capital Beltway? The South Capitol Street Bridge? The Pennsylvania Turnpike?

All these one-time symbols of "relief" are now rush-hour nightmares for commuters.

It therefore becomes necessary for legislative bodies to recognize that there is a limit to how many tax dollars can be poured into highway construction. And when highway funding is curtailed, it follows that substitute means of transportation must be provided. In this case, travel by bus must be encouraged.

So the government must intrude into our lives and pressure us into using the bus more, and private autos less. The rationale is much the same as it is for the government's intrusion into our lives when we are inclined to do foolish things like take unsafe or unprescribed drugs, threaten to jump off bridges, carry concealed weapons or consider buying shares in a company that says it has invented a perpetual motion machine.

From time to time, a "noble experiment" in governmental protection fails to produce a good result, and these occasions remind us that it is not always possible to protect a fool from the consequences of his felly. But we sure do try.

Democratic governments have a genuine concern for the welfare of their citizens. Their goal is to achieve the greatest good for the greatest number of people.

So for a government such as ours, the question is: "How much regimentation can be imposed without intruding unreasonably into personal freedom? How much protection is too much?"

The policemen assigned to Ron's route are there to keep traffic moving under rules worked out by legislators. Patroling the bus lanes is only one of their assignments. If their presence irritates these motorists who cannot or will not switch to mass transit - well, Americans have an opportunity to express their displeasure about such things on election day.

Is it idiotic to leave a lane open for buses on some highways?

I don't think so. I think the general principle of establishing bus lanes makes sense, even though its application in some specific instance may not.

Each bus lane that remains underused brings us back to the basic traffic question for these times:

For how many more years will commuters be able to drive to work in their individual autos before it becomes necessary to pave the entire countryside and make one big super-highway of all the open land between Suburbia and our central cities?