The Federal Housing Administration has raised doubts about the safety of homes near power transmission lines and now has made it a bit more complicated to buy and sell such houses.

Earlier this year, the FHA said it would refuse to insure mortgages on homes near the power lines. But after protests from homeowners who were unable to sell their homes and from the electric power industry, the FHA retreated.

Now the FHA says it will insure such houses, but is leaving it to lenders seeking federal mortgage insurance to obtain documentation that the lines meet construction or safety codes.

The FHA said it is concerned that transmission lines will fall on houses or nearby structures, such as swimming pools or storage buildings, and either set them on fire or electrocute people in them. It is also worried that the towers the transmission lines are attached to will fall on the houses or structures.

This spring, the FHA revised its appraisers' handbook for the first time since 1973 and included in it a provision that prohibited federal mortgage insurance for homes within 10 feet of an easement of a high-voltage transmission line and for homes close enough for a tower to fall upon them.

That prohibition previously had been issued through an agency memorandum, and the FHA appraisal form has long included an item that notes a house's proximity to transmission lines. But it was not until the prohibition became well known, as a result of being incorporated into the revised handbook, that problems arose.

The FHA and electric utility trade groups soon began receiving complaints nationwide from homeowners who were unable to sell their houses because of the restriction on mortgage insurance.

"We received several calls from our members who were concerned what the purpose {of the ban on insurance} was," said Larry Brown, an attorney with the Edison Electric Institute, a trade group for investor-owned electric utilities. "They heard it was being applied to the detriment of people selling homes."

Larry Hobart, executive director of the American Public Power Association, which represents government-owned electric utilities, said it had received complaints from the Phoenix area. "It is rather unlikely that you will have the problem that FHA is looking at," he said.

The FHA has no data on how frequently transmission lines fall on houses or how often towers fall, although it points to Hurricane Hugo, which struck the coast of the Carolinas last year, as evidence that transmission towers and lines can be toppled by the forces of nature.

The National Fire Protection Association, a group that sets fire code standards, does not keep statistics on fires caused by these kinds of accidents, noting that electric transmission facilities seldom are the source of fires.

"It is a thing that occurs rather rarely," said the Edison Institute's Brown.

Last month, the agency rescinded the guideline and directed its appraisers to use their discretion in assessing the safety of homes near transmission lines, using construction codes as their principal guide.

The FHA wrote that "if the appraiser notes any unsafe conditions, it shall be the responsibility of the mortgagee to insure that certification is received from the appropriate utility company or local regulatory agency that the property conforms to local standards and is safe or the unsafe conditions have been corrected prior to the request for insurance endorsement."

That is, the lender must secure documentation that the house has been built a safe distance from the transmission line, with safe distance being defined in local or state construction codes or, if there is no applicable code, by the National Electrical Safety Code, a non-binding standard used by industry.

Federal and industry sources said they did not know how many houses are near transmission lines, but the large poles and the lines are a fixture in many subdivisions, including some relatively new developments in the Washington area, such as at the Virginia Run complex in Fairfax County. The transmission lines extend 620,628 miles throughout the country. They carry large quantities of electricity through the utility network. Distribution lines, which take power off the transmission lines and deliver them to homes, are not covered by the new guidelines.

One leading private mortgage insurer, Mortgage Guaranty Insurance Co., does not assign the same risk to falling transmission lines as does the FHA. As long as there is no obvious hazard, mortgage insurance will not be held up because of transmission lines, said Joe Birbaum of that firm's residential underwriting department.

"If the FHA doesn't want to insure those mortgages, we'll be happy to," he said.