Worried about land speculation and uncontrolled growth around the Kennedy Library, a number of city planners and Cambridge civic leaders are informally suggesting the creation of an urban renewal project in the vicinity of the Library.

They reason that the presence of the Library on the Bennett St. MBTA Yards will raise land values in adjoining areas and encourage disjointed growth in the Brattle St. area.

"It would be a shame to have speculators come in, pay $30 a square foot for the land, and then have to build a very high-density building to get their money back," one man said yesterday.

Under urban renewal, they believe that Cambridge, through its Redevelopment Authority, would be able to control new construction in two basic ways: first, it would have to approve any new development within the area; and second, using federal money, the Redevelopment Authority could sell land at below-market costs.

The urban renewal idea has been discussed informally by the Citizens Advisory Committee (CAC)-a private group that advises the City on urban renewal-and the Cambridge Planning Board. The proposal has not yet been studied in detail, however, and most observers, including its partisans, see a large number of problems.

First, they say, the area around the Bennett St. Yards does not seem notably "blighted" and might not easily qualify as a renewal project. If the actual Bennett St. Yards were included in the project area, chances might be better. However, I. M. Pei, architect for the Library, does not favor putting his construction site under federal renewal laws.

Second, urban renewal has not been popular in Cambridge, and proposing a project might arouse political opposition.

Qualified observers have mentioned a variety of other problems in connection with the project. It has been suggested that Cambridge might exercise control over the areas around the Library by creating a so-called "Historical District" instead of a renewal project.

One local city planner has pointed out that the City can already exercise some control through its building and zoning codes. But partisans of the renewal idea believe that even greater control is needed. "The Redevelopment Authority," said one man, "can be a lot stricter than the zoning and building codes."