Hold the highway salt. A road de-icer made from landfill runoff could substitute for the salt that corrodes cars, bridges, and underground cables and contaminates ground water.

IT'S a regular occurrence at a hundred and more sites around New York City every day. Consolidated Edison workers go below the streets to repair underground electric cables. Corrosion is the problem, road salt the culprit. Keeping the city's streets free of ice in winter is not cheap. The cable-repair bill runs into the tens of millions of dollars each year, a burden that simply adds to the price of energy in the city.

But this scenario needn't continue. In some eyes, a solution may even lie as close as Staten Island ... in the leachate or fluid formed in and flowing from the Fresh Kills landfill.

The reason: calcium magnesium acetate (CMA), which can be readily processed from the leachate, is the Federal Highway Administration's ``de-icer of choice.'' CMA won federal approval because of its minimal impact on the environment.

A development program that could make biological extraction of CMA from woody and other waste materials an attractive commercial operation is about to begin. It involves the New York State Energy Research and Development Authority, Northeastern University in Boston, and the Universities of Syracuse (New York) and Georgia.

Conventional CMA is extracted chemically from natural gas and currently runs about $600 to $650 a ton, compared with $25 a ton for common road salt. But the true comparison is vastly different, when the environmental impact of the corrosive road salt is factored in, according to Lawrence R. Hudson, of the New York authority. When the costs of rusted autos, deteriorated concrete bridge structures, corroded reinforcing steel and cables, damaged roadside vegetation, and polluted drinking water are included, ``The real cost for road salt is nearer $2,000 a ton,'' he says.

In New York State alone, according to a report at the Solar '88 convention in Cambridge, Mass., last June, ``The deleterious effects of road de-icing cost more than $500 million a year.''

But bringing down the per-ton price of CMA is crucial to its widespread use. A very real possibility of reducing the cost of CMA is to let anaerobic bacteria extract it from waste. More significantly, such a process would ensure adequate supplies of the preferred de-icer, which could otherwise become scarce with even a partial move away from common salt.

No new technology is involved in this form of CMA production, according to Donald L. Wise, Cabot professor of chemical engineering at Northeastern, who wrote the original proposal for the program. Rather it involves pulling together established technologies.

CMA is made by stopping anaerobic digestion one step short of producing methane gas. At this stage the liquid extracted is largely acetic acid, which is passed over dolomitic limestone to form calcium magnesium acetate. This is then air-dried to form a granular substance that can be spread like conventional salt on icy roadways.

In several states, CMA is already mandated as a road de-icer even though supplies are not yet adequate. In these states, legislation generally bans the use of common road salt ``whenever supplies of CMA are available.'' Illinois is one such state, though it is pinning its hopes on the extraction of CMA from corn.

Dr. Hudson would prefer to see corncobs and other cornfield waste used in preference to corn itself, but the process that yields economic quantities of the de-icer from waste will also work with grain.

In New York woody biomass, including pulp- and paper-mill waste, is the most freely available raw material for the process and will be use primarily in the development program. Whey, the leftover liquid from cheesemaking, is another option, as is garbage. Dr. Wise takes the thought one step further and includes leachate from existing landfills. ``It's fermented, already partway to becoming CMA,'' he points out.

Wise has been closely associated with methane extraction, ``but right now we cannot make the gas as cheaply as natural gas can be extracted,'' he says. So he sees biologically produced CMA as an ``economic alternative'' to methane production and competitive with CMA derived by chemical means from natural gas.

Currently various landfills around the country are being tapped for their methane. Fresh Kills is one such site. Even so, leachate continually escapes from the site ... a pollutant with the potential to reduce the cost of maintaining electrical service in New York City.