The Montgomery County Housing Opportunity Commission is scrambling to get another corporate partner for an innovative program that would exchange special federal tax credits for money to buy lower-income rental town houses.

The search for a new partner came after a subsidiary of the Potomac Electric Power Co. rejected what housing officials had assumed to be an impending deal.

Tom Welle, a Pepco spokesman, said that Potomac Capital Investment Corp. (PCI) late last week rejected the housing commission's proposal to form a partnership to buy 30 town houses this year and additional town houses over the next two years.

PCI decided the proposal "does not fit within the company's business plans," Welle said. Neither Welle nor other company officials would elaborate.

PCI, established in 1983 as Pepco's investment division, mostly buys and leases aircraft, satellites, subway trains and buses to airlines, telecommunications companies and transit authorities, according to Welle.

The proposal called for PCI and the commission to form a limited partnership in which PCI would provide the money to buy town houses that the commission is authorized to purchase under the county's Moderately Priced Dwelling Unit program.

Under that program, builders in developments of 50 units or more sell 15 percent of the units at below-market prices to first-time home buyers. The commission has the right to purchase up to one-third of those units at cost.

In exchange for providing money to buy the town houses, PCI would have received federal low-income housing tax credits created by Congress in the Tax Reform Act of 1986 to encourage such housing.

The law allows companies to write off 9 percent of a project's acquisition or construction costs over 10 years against other tax liabilities.

The commission would manage the town houses, which, to qualify for the tax credits, would have to be leased to people who earn 60 percent or less of the area's median income at rents that could not exceed 30 percent of their income.

The units would have to remain rental housing for 15 years.

In Montgomery County, where the median income is $44,000 a year, a family of four earning $26,400 annually could qualify for a town house and would pay no more than $660 a month in rent.

Commission officials had counted on PCI's involvement to help alleviate an affordable-housing crunch in the county that the agency has been hard-pressed to solve.

According to a report released in July, the commission has a list of 5,588 households waiting for space in one of the agency's subsidized units.

PCI's decision surprised commission officials, who had taken company officials on a tour of the town houses throughout the county just days before and had expected PCI to agree to the deal.

"We wanted to close the deal. It's real important to us, and we're disappointed that we haven't been able to so far," said commission chairman James Brodsky.

Joyce Siegel, a spokeswoman for the commission, said "Pepco had been very favorable about it." She said the commission did not know why PCI backed out of the deal.

The commission now is under increased pressure to find another partner and sign an agreement before the end of the year. In order for a company to get a tax credit for 1987, the houses must be occupied by the end of the year.

Congress structured the program to last for three years. Each year's allotment of credits, which the states allocate to various agencies and developers, must be used during that year. Otherwise, the credits are lost.

Four out of seven companies that Montgomery's housing commission had approached with its tax credit program had expressed interest in it, but the companies "were put on the back burner" when the commission started "dealing seriously" with PCI in August, Siegel said.

"We have to go and pick up where we left off. We are actively pursuing this {discussions with other companies} because ... we don't want a drop of this potential housing credit to be lost," said Brodsky.

Welle agreed that the program had originally looked like an attractive investment for the company.

"But PCI didn't give them any signal that the company was ready to go ahead with the investment," he said.

Dale Riordan, executive vice president for administration and corporate relations for the Federal National Mortgage Association, which recently invested more than $30 million in low-income housing tax credit partnerships in three cities, said that Fannie Mae expects to make money over the life of the partnership.

"And there's nothing unique about Fannie Mae that makes the credits a good economic investment," he said.

But Patricia Payne, rental housing programs director for Maryland's housing and community development agency, said that tax credit projects leave investors vulnerable to the possibility of having to pay back the credits if tenants fail to meet eligibility requirements during the required 15-year rental period.

Brian Trossen, director of real estate advisory services for the accounting firm Laventhol and Horwath, said that, "although the tax credits are attractive by themselves, the deal that secures the tax credit may not be a sound investment. Low-income housing in general is risky."

He added: "The greatest uncertainty is what the property will be worth after 15 years" because of "wear and tear." The corporate owner, despite renovating, may not get what it puts into the property if it decides to sell the property.

Trossen also pointed out that many companies "don't want to potentially be seen in the media as displacing low-income people if they have to sell the property."