Gov. John A. Volpe pledged yesterday that the state "would start from scratch" in selecting a route for the Cambridge segment of the Inner Belt.

For opponents of the eight-lane highway, the governor's announcement was an important victory and a significant setback for the Brookline-Elm St. route. This route, fought for years by the City, threatens to go straight through Cambridge's largest commercial district -- Central Square -- and uproot between 3000 and 5000 residents.

Despite repeated attempts to convince the State Department of Public Works to select another route, Massachusetts officially recommended that the federal government approve Brookline-Elm last March. Now, about a month before the state elections, Volpe appears to have reversed his administration's decision, or, at least suspended it.

To make the governor's change official, DPW commissioner Edward J. Ribbs yesterday telegraphed the U.S. Bureau of Public Roads and asked for a delay of any decision on the Belt.

Working with a special committee from Cambridge, the DPW will now study plans for a Portland-Albany St. alignment for the highway. The designers of this route, a private group of planners called the Cambridge Committee on the Inner Belt, claim that it will displace both fewer jobs and families than the Brookline-Elm route. The Portland-Albany St. path is located East of Central Square just beyond the outer edge of the campus of the Massachusetts Institute of Technology.

The proposal is not new. It was presented last year, in substantially unaltered form, to the DPW, which said it studied the plan and then formally rejected it.

Yesterday's development left one large question in the minds of opponents of the highway. How serious would the review by the state DPW be?

Two members of the Cambridge Committee on the Inner Belt said last night that they would refuse an invitation to work with the DPW unless Volpe made it clear that he had "irrevocably rejected" the Brookline-Elm route. The two men, Denis Blackett and Robert Goodman, declared in a statement:

"The issue is simply and clearly whether or not the Governor is willing to reject a route which will displace over six per cent of the City's population and disrupt low-income, integrated neighborhoods." They said they would see Volpe and the DPW soon.

Volpe's move came as an election-year campaign against the Belt gathered momentum. Last Monday, the Cambridge City Council passed a number of resolutions against the Belt. Edward McCormack, Volpe's opponent, has already come out against the Brookline-Elm route, and a march on the State House had been scheduled for October 15. The march was still planned last night, but one leader commented "we certainly can't make it an anti-Volpe march."

Another factor considered by leaders of the anti-Belt campaign is the reaction of M.I.T. to the apparent new strength of the Portland-Albany route. Last winter, the Institute vigorously opposed another route (the "railroad alignment") nearer to the campus as well as the Portland-Albany location. It is not known, however, whether the Institute's opposition to the Portland-Albany route is as firm as its opposition to the railroad location