If recent experience is any harbinger of the futures solar energy may have a long, dark road ahead of it.

Consider the two demonstration projects begun by the Department of Defense three years ago with $3.1 million from the Department of Energy. The first project was to install solar heaters in 50 homes on U.S. military bases, the second to follow up with a different kind of solar heater at 80 homes on three different bases.

The first project is already dead, killed by a classic misunderstanding of how much money the heaters would cost. The second project is now threatened with imminent death, showing same symptoms that ended the first project.

"Neither DOD nor DOE established a formal system to monitor the progress of the project," the General Accounting office said in a report just released. "There is little assurance that problems similar to those which led to termination of the first project will not arise."

What happened the first time? The GAO said that everything went along dine until the Defense Department began to negotiate contracts with builders to install the solar collectors it had already designed and bought for $500,000.

The Defense Department estimated a cost of $50 a square foot for collection installation, only to find that no private builder would take the job for less than $200 a square foot. Even builders financed by the Small Business Administration placed low bids of $87 a square foot, unacceptable to the Defense Department.

Before terminating the first project, which it did last summer, the Energy Department gave the Defense Department $1.4 million to begin its second project. The only difference between the two projects was that the 80 homes were to get their solar heat from central solar collector "fields" located apart from the 80 homes.

This time, the Defense Department has not estimated the square foot cost for installing the collectors. But GAO says installation might be even more expensive than the first project's costs because the heat trapped in the solar "field" will have to be transported to each of the 80 houses.

"Minor costs overruns," the GAO said, "could please DOD in the same situation it had with the first project if the original cost objective is used.

The way these solar-heated house project are faring is reminiscent of two celebrated solar-heated skyscrapers in New York. One was the RCA building in Rockefeller Center, which years ago but never did because costs was going to get a solar tower four flew right off the roof.

More recently, the Citicorp building on Manhattan's East Side was fitted with a huge slanted roof, facing south to catch the sun's ray's. The building owner's $186,000 to study how best to convert the roof to solar heat-National Foundation had given the years ago when the costs for doing so but the plan was abandoned two were found to be $1 million.

Meanwhile, the Defense Department is trying to salvage some of the funds it got from the Energy Department for its first solar heating project. It has asked for and received permission to divert $615,000 of leftover money into other solar projects, including $71,500 to use solar collectors to dry out wet parachutes. Post