President Carter's plan to insulate and solarize America's homes may prove harder than it sounds. Experts raise some serious doubts about the program's timetable and costs as we as the protection of consumes who use its tax credits to install insulation and solar heating equipment.

The doubts arise because the President gave the nation less than eiht years to reach his goals on insulation and solarization, because the costs of doing both are on the riseandbecause the business of doing both could involve the participation of contractors with little regard for building codes and standards.

The President's program call for the insulation by 1985 of 90 per cent of America's 53 million homes, which means insulating in a little more than seven years mot of the 40 million homs the Federal Energy Administration identifies as "under-insulated."

Not even the nation's insulation makes believe this goal can be met. The three leading producers of fiberglass insulation and the nine largest producers of mineal and rock wool insulation are prdocucingallthey can now, and even a doubling of plant capacity by Johns-Manville (the largest producer) in the nexttwo years will not met expected demand.

"THe entire industry igures it can insulate no moe than 1.5 million new starts and four million retrofits a year at the peak," Johns-Manville's David Pullen said yesterday. "And that's startng two years from now. Frankly, awe recommended a 10-year program, not seven years."

Carter would offer homeowners a tax credit of 25 per cent of the first $800 and 15 per cent of the next $1,400 they spend on insulation, but costs are rising so fast that they might soar beyond the reach of the tax credits.

The fiberglass that makes up 70 per cent of theinsulation materials used in the United Sates rose in price 50 per cent in the last three years. The FEA said that floors and attics that cost $200 apiece to insulate a year ago now cost $250 each. Walls of a 1,300 -square-foot home cost as much as $600, bringing the cost of insulating (excluding storm doors and windows) an average home to more than $1,000.

Carter's goal for solar energy is 2.5 million homes by 1985, which solar energy experts claim is less realistic than his timetable for home insulation. The President did not spell out what he meant by solar "equipment," but presumably he meant water and space heating machinery.

"That goal will be exceedingly difficult to meet," said Dr. Robert L. Hirsch, deputy scientific manager at Exxon Corp. in New York and until three months ago director of solar energy programs at the Energy Research and Development Administration. "There are an awful lot of problems it faces."

Not the least of these is the cost of machinery and the cost of installing it in the average home to use the sun's heat to warm water and the entire house. It now costs as much as $2,000 to install a solar hot water system in a new home and 25 per cent more if it's out in existing home, where panels, walls and plumbing have to be ripped up and redone.

Carter promised a tax credit of 40 per cent of the first $1,000 and 25 per cent of the next $6,400 spent on solar home installation, but if homeowners want more than solar hot water machinery they will pay a lot more than what's covered by the credits.

Solar hot water systems require just a few square feet of solar collectors on a south-facing roof, but a solar space heater takes up an entire side of a roof. It now costs as much as $60 a square foot for these collectors in new homes and $75 in old homes.

The cost of installing plumbing that can circulate water through vast regions of the house has risen because manufacturers found that "hard" water in most parts of the United States ruined the aluminum pipes and collectors they began to use. They now use brass and stainless steel, which have forced solar heating costs to between $12,000 and $15,000 a house.

Another problem with solar heating is that it needs more sunshine than solar hot water systems, limiting its use to six months a year in colder parts of the country. New York City turned down solar heating for municipal buildings a year ago because of this.

Finally, there's the question of consumer protection. Solar building codes and standards are at least two years away, meaning there are none now to protect homeowners against fraud and won't be any until at least 1979.

"The tendency of the federal government is never to get involved in consumer protection standards," Exxon's Hirsch said. "The trouble with that is you end up fostering with tax credits an industry that doesn't have to operate under any standards."