THE ATTORNEY GENERAL'S Task Force on Crime was asked to study a subject that had already been studied about as thoroughly as any public policy issue can be. Most of the ideas it has adopted have therefore--inevitably and unsurprisingly--been heard before. The value of the work of this group, headed by former attorney general Griffin Bell and Gov. James Thompson of Illinois, lies not in the novelty of its recommendations but in the possibility that its report can become a rallying point for those who want to do something about crime.

The most highly publicized recommendation is an example. The task force wants the federal government to spend $2 billion to help the states build more and better prisons. That sounds much like a proposal Sen. Bob Dole put forward a couple of years ago and much like a major theme in Chief Justice Warren Burger's call last winter for a national war on crime. But will the Reagan administration, with its eyes focused on cutting government costs, show much enthusiasm for such a burst of spending? If it doesn't, how are the states to come up with that kind of money, given the additional costs the federal government is already handing back to them?

Many of the task force's other recommendations have a similar history. Its proposal for changing the sentencing system is quite similar to that introduced some time ago by Sen. Edward Kennedy in the federal criminal code bill. Its proposals for revamping the exclusionary rule and reinstituting preventive detention follow a well-marked, if highly controversial, path. Its handgun proposal is so old no one remembers when or where it originated.

The test of the work of this group, and of any counterattack on crime launched by the Reagan administration, will not be how many of these recommendations eventually go into effect, but rather which ones do. It is easy to find among these proposals a collection that would provoke a gaudy battle on Capitol Hill, but which, if enacted, would make only a cosmetic difference in the crime situation.

The simple truth is that Washington can do little to make the nation's streets safer other than provide money for state and local governments. Outside the District of Columbia, the jurisdiction of the federal government over the kinds of crime that leave citizens fearful is quite limited--and properly so. A new federal preventive detention law, for example, could be hailed as a great anti-crime mea sHOure, but it would affect only a tiny handful of those cases involving murder, rape, robbery or burglary.

If this administration is serious in its talk of attacking the crime problem, it will not shy away from the task force recommendations that cost money (improving penal facilities) or enrage some of its supporters (handgun controls). If the administration ducks these matters and focuses instead on things that don't cost money (like modifications of federal court rules), it will miss a great opportunity to do something substantial about violent crime.