Montgomery County Council President Rose Crenca said she has decided to temporarily shelve a bill that would require all homes sold in the county to be tested for radon after hearing testimony against the proposal this week. "I was impressed by the testimony," she said. "I don't believe there is support now for the bill from other council members."

The bill would require homes sold after Jan. 1 to be tested for radon and, starting next June 1, would require homeowners whose houses exceeded acceptable radon levels to solve the problem before being allowed to sell their homes.

The decision to table the legislation comes at a time of growing public concern about radon, a colorless and odorless radioactive gas produced by the breakdown of uranium deposits in the soil.

Radon, which can seep into houses through cracks in basement floors and walls and has been estimated to cause between 5,000 and 20,000 lung cancer deaths a year, is believed to be the leading cause of lung cancer in nonsmokers.

John Menke, director of the county's environmental protection department, who represented County Executive Sidney Kramer at the hearing, testified that testing methods are not foolproof.

He said that the most common testing method, which involves placing a charcoal canister in a basement of a home for three or four days, could allow sellers to tamper with the results merely by opening windows and doors to ventilate the house.

He advocated voluntary testing agreements between buyers and sellers rather than county-mandated tests.

Thomas Sheahen, president of Western Technology Inc., a county engineering and consulting firm, said that radon levels fluctuate with weather conditions and can change radically depending on the day and season.

During periods of low air pressure, for instance, radon levels can rise dramatically.

Consequently, "a shrewd real estate agent only has to wait until a day when the rain stops and the sun begins to shine to rush in and to make a radon measurement" to produce favorable test readings, Sheahen said.

Bill Sonntag, a spokesman for Suburban Maryland Building Industry Association, also testified that only testing at various times of the year can reveal a meaningful result.

"Testing during the period of real estate transactions is inadequate," Sonntag said.

Alleviating high radon levels is "relatively inexpensive," he testified.

Sheahen said the cost to correct the worst cases of radon merely involves drilling a hole through a concrete slab and venting it outside.

Such a subslab ventilation system costs about $1,200, he said.

Crenca said she will delay action on the bill until the county's environmental protection department completes a study on the extent of the radon problem in the county.

That isn't expected to be completed for another six months, Crenca said. The National Council of Savings Institutions has found in a survey that most thrift institutions do not want to stop or slow the growth of the number of loans that are eligible for purchase by federally sponsored agencies in the secondary mortgage market.

The Federal National Mortgage Association (Fannie Mae) and the Federal Home Loan Mortgage Corp. (Freddie Mac) currently purchase mortgages of up to $153,100, a figure that will automatically adjust upward on Jan. 1 based on the average national increase in housing prices from October 1986 to October 1987.

Some lenders have voiced concern that Fannie Mae and Freddie Mac had begun to dominate the mortgage market at the expense of the private secondary market.

But the savings institution trade group said that in a survey of about 300 savings and loan associations and savings banks in late July and early August, officials voted by a 3-to-1 ratio in favor of allowing the size of the loans eligible for purchase to continue to rise.

"From most lenders' point of view," National Council chairman John T. Morgan said, "the federal secondary market agencies provide thrifts with important sources of fee income through {loan} originations and servicing of mortgages.

Fannie Mae and Freddie Mac are often the only option for thrifts, which due to their size or geographic location -- do not have sufficient access to private secondary markets." IN THE BUSINESS ... The Shady Grove Executive Center, a joint venture of Spaulding & Slye, IBM and Copley Real Estate Advisors, has started construction of three new buildings, two of which will be leased to IBM and the third of which is a speculative venture. All three of the buildings are 120,000 square feet. ... A group of real estate developers and others in the real estate industry have formed the I-270 Partnership to attract more businesses to the Montgomery County corridor and to encourage those companies already there to expand their operations. ... Marriott Corp. has started construction on its fifth Courtyard by Marriott hotel in the Washington area, this one in Silver Spring on Prosperity Drive at the intersection of Route 29 and Randolph/Cherry Hill Road. It is expected to open next fall. ... Trammell Crow Co. is building an 84,000-square-foot shopping complex called Annapolis Fashion Festival on Jennifer Road in Annapolis. ... Emory Hill McConnell Associates, a Delaware-based developer, has started construction on a $5.5 million office building at 10010 Junction Dr. in the Junction Business Park in Howard County. ... PRC Realty Systems of McLean, which provides computerized multiple listing service systems to Washington area Realtor boards, has signed a letter of intent to buy MultiList Inc. of Denver, which provides similar information systems and photo listing books to about 80 Realtor boards and multiple listing service groups throughout the United States. ... McShea & Co. Inc., a Gaithersburg development firm, says that it plans to develop the North Amber Business Park in Frederick. The park is a six-building complex. ... The Fredericksburg Area Builders Association opened its fifth annual Fall Parade of Homes yesterday. It runs through Oct. 4. The 27 new homes are at various locations throughout Stafford and Spotsylvania counties and range in price from $70,000 to $200,000. For more information, call 703-898-2730. ... Howell Properties of Virginia has acquired Mary Price Realtor of Falls Church. ... The Suburban Maryland Building Industry Association's institute for professional development has scheduled a 40-hour program on commercial real estate development from Oct. 13 to Dec. 8, as well as a five-week series of half-day introductory seminars on the building process starting Oct. 16. Call 572-5900 for more information.

PERSONNEL FILE ... Winchester Homes Inc. has promoted Christopher Zell, its corporate marketing director for the last 2 1/2 years, to vice president for marketing. ... Nancy Bryant has been named executive vice president of the Society of Industrial and Office Realtors. ... Thulman Eastern Corp., an Ellicott City-based distributor and manufacturer of housing products, has named Dennis Rothouse as president of its mid-Atlantic region.