July 22 (Bloomberg) -- Federal Reserve Chairman Ben S. Bernanke said a potential wave of defaults in commercial real estate may present a “difficult” challenge for the economy, without committing to additional steps to aid the market.

Bernanke, testifying before the Senate Banking Committee today, urged lenders to modify “problem” mortgages to avert defaults. Christopher Dodd, the Connecticut Democrat who chairs the panel, told Bernanke that “some have suggested” the commercial market “may even dwarf the residential mortgage problems” in the U.S.

The state of commercial real estate was one of the most- asked-about subjects in questioning by lawmakers so far in Bernanke’s two days of testimony on the economy. Bernanke said today in the Senate and yesterday at the House Financial Services Committee that it’s too early to tell how effective the Fed’s main initiative in the area will be.

The Term Asset-Backed Securities Loan Facility, a Fed emergency program that lends to investors to purchase securities backed by consumer and business loans, began accepting commercial mortgage-backed securities as collateral last month.

Fed policy makers will extend the TALF, currently scheduled to expire Dec. 31, should they judge financial markets are still “some distance from normal operation,” Bernanke said today.

TALF Extension

“We will certainly be monitoring the situation, and if markets continue to need support, we will be extending the final date of that program,” Bernanke said.

It “may be appropriate” for the government and Congress to consider “fiscal” steps to support the industry, Bernanke said today. Ideas for fresh support for the market could include government guarantees for commercial mortgages, Bernanke also said today, while noting no proposal on the subject has emerged.

U.S. commercial property prices fell 7.6 percent in May from a month earlier, bringing the total decline to 35 percent since the market’s peak, Moody’s Investors Service said in a report this week. Commercial properties in the U.S. valued at more than $108 billion are now in default, foreclosure or bankruptcy, almost double than at the start of the year, Real Capital Analytics Inc. said earlier this month.

Yesterday, more than a half-dozen members of the House panel mentioned or asked Bernanke about the topic, with Chairman Barney Frank saying there’s a “great deal of fear” that a wave of commercial defaults will produce economic problems similar to those caused by residential mortgages.

“As the recession’s gotten worse in the last six months or so, we’re seeing increased vacancy, declining rents, falling prices -- and so, more pressure on commercial real estate,” Bernanke said yesterday. “We are somewhat concerned about that sector and are paying very close attention to it. We’re taking the steps that we can through the banking system and through the securitization markets to try to address it.”

One of the main issues for the industry is that the market for debt backed by commercial mortgages “has completely shut down,” the Fed chief said yesterday.