Serendipity has reared its lovely head in the Supreme Court, illuminating the continuity of our constitutional life. At the close of the court's term this bicentennial summer, there came a case that turned the court's mind, like the needle of a compass, to the kind of question that vexed the Constitution's framers.

In 1982 Congress declared that a percentage of federal highway funds should be withheld from states that do not have a drinking age of 21. Congress was addressing an obvious problem: young people drink and drive when they drive across state lines in quest of drink.

South Dakota, where 19-year-olds can drink 3.2 percent-alcohol beer, decided that Congress' action was inconsistent with the Constitution's allocation of powers. South Dakota cited the 21st Amendment, which repealed Prohibition and gave states the power to regulate alcohol. Now, South Dakota rising in righteousness is a stirring sight, but if the state thought it had a chance of winning, it has been drinking stuff stronger than ''near beer.''

Justice O'Connor, dissenting (the only other dissenter was Justice Brennan), acknowledged that Congress may attach conditions to the receipt of federal funds. However, she said, the conditions must be reasonably related to the purpose of the particular federal program. And she said the establishment of a national drinking age is not ''sufficiently related to interstate highway construction.'' Surely she was wrong. Safe interstate travel is a goal of the highway program.

Chief Justice Rehnquist, in a limp opinion for the 7-2 majority, skirted the large, interesting issues. He said the withholding of a piddling 5 percent of South Dakota's highway funds is tolerable. But, he added, anxiously, there might be a financial inducement so coercive as to turn a mere incentive into compulsion.

Such hairsplitting miniaturizes the disputes. Better he had said: ''Colorado and South Dakota will soon be in compliance with Congress' wishes regarding drinking. Only Ohio and Wyoming remain defiant. A Cromwellian approach is needed for the two recalcitrant legislatures. Paratroopers deployed with fixed bayonets along the walls of the legislative chambers should suffice.''

Just kidding. But seriously, folks, it is fun, 200 years into our experiment, to see a continuation of the old debate on the nature of the sovereignty of the central government.

Rehnquist was right as far as he went, but his argument lacked vim. The court should have seized the occasion for a thumping affirmation of Hamiltonianism.

However, before Rehnquist was elevated to the glory of the court, before he put aside all merely political philosophy in favor of constitutional doctrines, he was a conservative of the Jeffersonian stripe. He was suspicious of the central government and hot for local authority and states' rights.

Ours is now a Hamiltonian country with, unreasonably, an uneasy conscience about that. It has a strong central government, as required for an industrial, continental republic. But the tuning forks in our minds vibrate most naturally to Jeffersonian cadences.

These following words (from O'Connor's dissent; she, like Rehnquist, is from Arizona, a haven of Jeffersonianism) are an example of Jeffersonian cadences: ''The immense size and power of the government of the United States ought not obscure its fundamental character. It remains a government of enumerated powers.''

Yes, yes, of course. But immediately after those words, O'Connor cited, as a source of the thought, the case of McCulloch v. Maryland (1819). However, it is we Hamiltonians -- we strong-central-government conservatives -- who applaud the McCulloch opinion written by Jefferson's great rival, Chief Justice Marshall. In it, Marshall firmly established the doctrine of the implied powers of Congress.

Yes, Marshall said, Congress has only enumerated powers. But Congress is entitled to considerable discretion ''with respect to the means by which the powers {the Constitution} confers are to be carried into execution.'' The central government's powers should be interpreted to comport with the central government's tasks.

If the task (e.g., promoting highway safety) is legitimate, all appropriate means adapted to that task not explicitly prohibited are permitted.

This small case was a timely and deeply satisfying bicentennial event. The 21st Amendment gives states the power to control alcohol. Is it legitimate for Congress to legislate an incentive for the states to voluntarily abridge their constitutional rights? The vocabulary for discussing even this minor matter drives us back deep into a perennial theme of our history: the tensions inherent in our system of limited, delegated, enumerated -- and implied -- powers. The presence of the perennial is soothing to the conservative temperament, which is pleased by continuities.