ASHINGTON — Lifetime tenure for judges was "the best expedient which can be devised in any government," Alexander Hamilton wrote in The Federalist No. 78, defending the Constitution's provision for judges to "hold their Offices during good Behavior." Of the wisdom of that proposition, he added, "there can be no room for doubt."

But an ideologically diverse group of legal scholars is now not so sure. Judicial tenure? Definitely. A long one? Probably. But life tenure, which increasingly translates into 25 to 30 years on the bench, extending into extreme old age? When it comes to the Supreme Court, at least, there seems to be plenty of room for doubt, and the doubts are growing.

Judges depart from the lower federal courts with regularity, assuring a steady turnover. Supreme Court vacancies, on the other hand, are rare events. It has been nearly 11 years since the last one, when Harry A. Blackmun stepped down at age 85 after 24 years on the court.

The trend is clear. From 1789 to 1970, the average Supreme Court justice served for 15.2 years and retired at 68.5. But since 1970, the average tenure has risen to 25.5 years and the average age at departure to 78.8.

In law review articles and commentaries that began as a trickle a few years ago and that now, as these things go, amount to a flood, scholars are questioning whether this is what the Framers had in mind. The modern justices' longevity "has fundamentally altered the practical meaning and implications of lifetime tenure," Professors Steven G. Calabresi and James Lindgren of Northwestern University School of Law have written in an unpublished article.

"We aim to dispel the myth that life tenure for justices is fundamental to our democratic self-government," they write, pointing out that only one state, Rhode Island, provides it for its supreme court judges and that every other major democracy has age or term limits.

The academic critics see a variety of negative consequences from life tenure. One is that the scarcity and randomness of vacancies promise to turn each one into a galvanizing crisis. Other drawbacks include the temptation for justices to time their retirements for political advantage; an overemphasis on youth and staying power as a qualification for nominees; the likelihood that even those justices who escape the infirmities of old age - and, predictably, not all will escape - will tend after many decades to lose touch with the surrounding culture; and the fear that if the court is seen as out of touch and unaccountable to a democratic society, its legitimacy will erode.

"The result is a situation of grave proportions needing correction," wrote two other law professors, Paul D. Carrington of Duke and Roger C. Cramton of Cornell. "Unchecked power, the Founders correctly believed, has a tendency to produce a degree of hubris and arrogance among those who exercise that power." They are circulating a proposal they call the Supreme Court Renewal Act.

Since life tenure is specified in the Constitution, most proposals for modifying it call for a constitutional amendment. But the Carrington-Cramton proposal is for ordinary legislation by Congress that the two professors believe would withstand constitutional challenge.

They propose giving Supreme Court justices lifetime appointments to the federal judiciary, but not specifically to the court. The president would be entitled to appoint one new Supreme Court justice during each two-year session of Congress - two nominees in each presidential term - without waiting for a vacancy.

That means, of course, that the court's total membership would grow. Under the plan, the nine most recently appointed justices at any given time would constitute the court's active membership; the rest would be "senior justices," performing temporary service as needed on other federal courts, much the way senior federal judges do today. Effectively, each new justice would be active on the Supreme Court for 18 years, before reaching "senior" status and being supplanted.

The proposal, which would not affect justices now serving, has been endorsed "in principle" by two-dozen law professors, including some prominent liberals and conservatives.

Staggered 18-year statutory terms also figure in proposals for constitutional amendments put forward by various scholars, including Prof. L. A. Scot Powe Jr. of the University of Texas, who, in an article five years ago, called life tenure "the stupidest provision in the Constitution," and Philip D. Oliver of the University of Arkansas.

Other proposals are more radical. Another Northwestern professor, John O. McGinnis, has suggested rotating federal judges through the Supreme Court for terms of six months to a year. Judge Laurence H. Silberman of the federal appeals court here has proposed a five-year rotation. (Age limits, as opposed to term limits, have found little favor.)

Is there anyone left to speak up for life tenure? Predictably, this being the academy, there is. "Life tenure is due for a fresh defense," Ward Farnsworth, a Boston University law professor, writes in an article to be published this spring in the University of Illinois Law Review.

Questioning whether a court that does not reflect the prevailing climate is really a problem, he observes that "one of the valuable things courts do is make unpopular decisions that stick." And Professor Farnsworth said he doubted whether term limits would really lower the political temperature: instead, he argues, they could magnify presidential power and make the two guaranteed appointments each term come to seem like the spoils of political victory. Professor Farnsworth warns of unintended consequences: "Life tenure has costs that we have learned to live with, and we ought to hesitate long before switching."

Granted, all this conversation is at this point largely academics talking to one another. But many of them are former Supreme Court clerks, and chances are their former bosses are listening in. Even if no actual bill or amendment is introduced in Congress, the behavioral norm on the court, having swung fairly quickly toward sticking around for decades, could be swung back again by the debate - and that may well be the point of the exercise.