THE HELL'S ANGELS don't like the idea of a seat belt law--and showed Cambridge as much by taking to the streets Saturday on their choppers, ironically, complete with police escort. Angels aside, don't be intimidated by the lobby against the state law that currently requires the use of seat belts, the lobby that called for "freedom of choice" and got a binding referendum to be put on Tuesday's ballot. In just one year since its approval by the U.S. Congress, the mandatory seat belt law has proven its worth; it deserves to stay.

Crying freedom of choice on this issue is like crying wolf. Driving is a privilege, not a right, and it is misleading to cast the question of whether drivers and their passengers should be fined $15 for not wearing seat belts purely in terms of personal liberties. Just as drivers give implied consent to be subjected to a breathalyzer test and so waive certain privacy rights, it is hardly unreasonable to expect them to follow a rule like the seat belt law which is not only in their own interest, but also holds down medical costs for taxpayers and insurance rates for all drivers.

Opponents of the law mistakenly focus on the act of buckling up instead of its context. A seat belt doesn't just protect the individual who wears it; its use means that the driver is taking seriously the privilege of driving and its concomitant responsibility. A mandatory seat belt law, in this sense, is like a speed limit.

The law does more than impose fines on citizens; it sets up state-sponsored education and police training programs. More important, the law can be enforced only if the driver has been stopped for violation of another motor vehicle law. For individuals who have already shown irresponsibility and have put others in danger, it is reasonable to make the enforcement of those other laws also a checkpoint for safety belts.

State Department of Public Safety statistics from the law's first year, moreover, show that it is effective. Serious auto injuries have dropped 23 percent, which means that 1706 fewer people have been hurt in the first eight months of 1986 than in previous comparable periods. A department survey showed that an estimated 35 percent of Massachusetts citizens now use seat belts, compared with 19 percent one year ago. It doesn't take a particularly complex calculus to justify a yes on Question 5.