President Carter's plan to force power plants and factories to burn coal instead of oil and gas would not increase total air pollution nationally, Environmental Protection Agency Administrator Douglas M. Costle said yesterday.

Increased pollution from industrial coalburning would be offset by energy conservation measures, such as home insulation, which would reduce the overall amount of fuel burned in power plants, he said.

Costle's optimistic assessment of the coal conversion program was greeted with skepticism by members of the Senate Environment and Public Works Committee.

"Your whole equation is premised on emissions savings from conservation," said Sen. Gary Hart (D-Colo.) "If you're wrong on that, its a whole different ball game."

Costle replied, "You are absolutely correct."

Sen. Edmund S. Muskie (D-Maine) said EPA figures do not show the effect of coal conversions on specific regions. "The fact is, since industry is mainly in urban areas, you'll increase exposure to pollution in the areas where most people live," Muskie said.

For example, a small industrial boiler that now runs on gas would emit 3,000 tones more sulfur oxides - which cause respiratory disease - if it is converted to coal as required by Carter's energy plan, he said.

Even if the industry used low-sulphur coal and a scrubber machine - which Carter's plan does not require - sulfur emissions would increase 300 times, Muskie said.

Depsite Carter's assurance that there will be no environmental trade-offs for energy, Muskie said it will "be a sure thing" that most urban areas will violate health standards if coal conversion occurs.

Costle acknowledged that "it's not going to be an easy transition." But he said cities could accommodate coal conversions by reducing pollution from other sources, for instance, by closing a municipal incinerator.

Coal conversion will mean that areas which have been lax in meeting air pollution laws will have to "buckle down and find offsets," Costle said. "They're going to be between a rock and a hard place."

Such areas include most of the Northeast, which once burned coal extensively, and cities such as Los Angeles and Houston where automobiles contribute substantially to air pollution.

"The most promising region for coal conversion is the Northeast," said Sen. Robert T. Stafford (R.-Vt.). "But that is also the area with the greatest [air pollution] problems."

Costle acknowledged that air pollution might preclude coal conversion in a few areas, such as the middle of New York City. "But you can go less than 70 miles outside New York City and find areas to locate a major coal-burning source with proper controls." he added.

Only 10 per cent of facilities affected by coal conversion legislation would be oil-or gas-burning plants that once used coal, Costle sai. New facilities, or plants that have burned exclusively oil or gas, represent 90 per cent of affected facilities.

Air pollution from an expected 200 million tons a year of increased coal burning would be reduced by legislation now pending in Congress to require the best pollution control machinery available on new coal-burning plants.

Costle said such a requirement, which would reduce sulfur and dirt particles by 50 per cent, would cost industry $4 billion and utilities $5 billion over the next eight years. It would result in a 1 per cent average increase in consumers electricity bills.

Sen. Malcolm Wallop (R-Wyo.) said that, with coal conversion, "heavy industrial area would have a franchise on the use of oil and gas. Areas like ours would have to sacrifice a clear air economy based on natural gas."