Federal Housing Finance Agency Director James B. Lockhart acknowledged that he is concerned that rising mortgage rates could deal a blow to the Obama administration's plan to help strapped homeowners.

"Certainly it is an issue. We're certainly seeing a slowdown in refinancings, you can see the numbers," Lockhart said in response to a reporter's question Thursday.

A key part of the administration's plan aims to help underwater homeowners refinance to take advantage of low mortgage rates. But rates have shot up to well above 5% since the program was announced. So far, 80,000 homeowners have received refinancings under the program.

"There's a big pipeline so it probably won't hit for a couple months," Lockhart said. "But at some point, if we don't see some moderation of rates, it could have an impact."

Lockhart, the regulator for Fannie Mae (FNM) and Freddie Mac (FRE), confirmed the administration is mulling tweaks to the program so homeowners with mortgages worth more than 105% of their home's value could qualify for refinancings.

He declined to say what the new loan-to-value limit would be, but said that loans with a 125% loan-to-value ratio could be sold into special pools known as Real Estate Mortgage Investment Conduits, or REMICs.

Lockhart said Fannie and Freddie were barred by their charter from engaging in "warehouse" lending, which nonbank mortgage lenders rely on for capital to make fresh loans. Lenders have seen their warehouse lines of credit cut due to the credit crunch.

Lockhart said Fannie and Freddie could help cash-strapped lenders by agreeing upfront to purchase the loans before they are originated.

- By Jessica Holzer, Dow Jones Newswires; 202-862-9228; jessica.holzer@dowjones.com