For years the Inner Belt Highway has been a nightmare for Cambridge. Now the City has awakened, but the nightmare hasn't gone away.

What the Inner Belt threatens to do is uproot nearly five per cent of the City's population and pass within two blocks of Central Square. The Inner Belt itself will have eight lanes and the service roads that must run parallel to it will add another four or six. Clearly, the prospect isn't either pretty or pleasing, and the City Council has consistently informed the Commonwealth of its opposition to "any and all Belt routes" through Cambridge.

But until a few months ago, that was the extent of the action. Meanwhile, over the summer, the state legislature took away any initiative the City might have had by removing its right to veto any route officially proposed by the State Department of Public Works. The veto was not absolute; any dispute would have gone to a three-man arbitration board with one neutral, one man appointed by Cambridge, and one by the DPW. Yet, despite its limited nature, the veto stalled DPW action on the Cambridge segment of the highway.

But the veto may not have been the only reason for the delay. The DPW was busy winning approval of routes through Boston and Somerville. Having done this and having had the partial veto successfully removed, the DPW has rendered Cambridge virtually powerless.

Despite this, Francis Sargent, commissioner of the DPW, has said that he will inform Cambridge of his decision before sending any official route to Washington for approval. (The Inner Belt is part of the Inter-State Highway System, and the federal government picks up 90 per cent of the cost.) Sargent has said that he wants to get the best route for Cambridge and wants to cooperate with everybody.

Even if Sargent's words represent more than political tact, there are good reasons for believing that the DPW is intent on selecting the Brook-line-Elm Street route--the one that would wipe out 1000 to 1500 families and run right next to Central Square. First, it has been the route long championed by his agency. Second, plans for this route are farther along than for any other. And third, any other realistic alternative would run along the fringe of the M.I.T. campus; the political power of M.I.T., a venus flytrap for federal research contracts, is latent, but great.

Basically, all the alternatives to the Brookline-Elm Street route run over or parallel to a set of abandoned railroad tracks in East Cambridge. The tracks themselves are owned by M.I.T., and if the Belt went along any of the proposed paths in this area, at least several M.I.T. buildings would get wiped out.

The DPW originally offered--and tentatively rejected--two alternatives in this area. Now a group of private planners, known as the Cambridge Committee for the Inner Belt, has refined these plans and charged that the original DPW designs were drawn so as to make them unacceptable. Their new plans take less land, fewer jobs, and fewer homes (only 150, the committee claims). M.I.T. has remained mum on the Inner Belt; it has not made (nor has anyone else attempted to make) an objective analysis of the disruption the noise and vibrations from a large highway would have on experiments. Clearly, the extent of this disruption--and whether there are ways to limit or eliminate it--should be taken into account if the "railroad" alternatives are to be considered seriously.

Whether they will be or not depends on a number of other factors:

* The City has sent the alternative plans to a highly-respected Chicago firm of traffic consultants. If the consultants say the new designs are technically acceptable, and if the City officially adopts them as preferable to the Brookline-Elm Street route, the DPW will be forced to take a second look.

* The quality of the City's opposition will also have a lot to do with the chances of the alternatives. Everyone knows Cambridge opposes the Inner Belt, and unless politicians--and, more importantly, residents--are able to demonstrate that this opposition is strong and determined, the DPW will be tempted to brush aside the alternatives. Even if the railroad alternatives prove unfeasible, public pressure may force the DPW to make the Brookline-Elm Street route as palatable as possible by altering the design and helping with relocation problems. Leaders of the public opposition to the Inner Belt ought to be prepared to show their strength by more than large numbers at City Council hearings. There is nothing that Boston papers like better than a big angry march.

One could, of course, argue that the Inner Belt is altogether senseless and unneeded. It may be. But this dispute has gone beyond that stage. There will be an Inner Belt through Cambridge, and regardless of where it is, the City stands to lose a great deal. But only by quick and effective action is there any chance of minimizing the lost.