THE QUESTION of jurisdiction - which cases a court can hear - lies at the heart of any legal system. On their way out of office the top lawyers of the Ford administration proposed removing from the jurisdiction of federal district courts about 40 per cent of the case they now hear. That would amount to a drastic overhaul of the nation's judicial system - nothing like it has been attempted, in fact, in 50 years.But the proposal itself it not new. Some members of the judicial branch, including the Chief Justice, have been recommending it for some. The difference is that they have now been joined by a committe drawn from the top ranks of the Ford Justice Department; and, if the testimony of Attorney General Griffin Bell is any guide, may soon be issued by the Carter administration. This, in turn, could bring Congress face to face with the necessity of either rearranging the American courts of sharply increasing the number of federal district judges.

The problem behind all this agitation is that the federal courts are being asked to do more than they can do. The social legislation of the last 15 years has led to more litigation than anyone dreamed it would. And added to this has been the growing tendency around the country to take to court every claim anyone can think of. There is no relief in sight. The Mine Safety Act, for instance, could generate more than 20,000 jury trials a year - a number that the existing court system simply could not handle.

The committee, which was set up at Mr. Ford's direction with Solicitor General Robert H. Bork as chairman, has made many specific proposals. The most important, in our views, recommends the creation of a federal administrative court system to handle claims under many, if not most, welfare and regulatory laws, ranging from Medicare and consumer products safety to Social Security and truth in lending under such laws involve repetitious questions of fact that must be resolved fairly but do not involve important questions of interpretation for which the federal district courts should be reserved. Many of these cases, it says, could be handled informally and without lawyers - and thus, more quickly and more cheaply if they were dealt with outside the regular court system.

The committee would also like to see two kinds of cases turned over to the state courts: those in which state prisoners claim their jailers are violating their constitutional rights and those which are in federal court only because the parties live in different states. Involved are about 36,000 cases a year, including a quarter of the jury trials now held in federal courts.

All this, of course, deserves careful scrutiny. But the proposals do seem to us to be positive in the right direction. Unnecessarily burdening the federal courts with routine cases undermines both their prestige and the quality of justice they can produce.