The Federal Reserve’s interest-rate cuts last month have failed to lower borrowing costs for many companies and households, increasing the chance of further reductions from the central bank.

Companies are paying more to borrow now than before the Fed reduced its benchmark rate by 1.25 percentage point over nine days in January, based on data compiled by Merrill Lynch & Co. Rates on so-called jumbo mortgages, those above $417,000, have increased in the past month, making it tougher to sell properties and risking further price declines.

“It’s the clogging up of the credit markets that worries me most,” a Harvard University economist, Martin Feldstein, said in an interview in New York. “The Fed has done a lot of cutting, the question is whether it’s going to get the traction that it did in the past.”

Lenders and investors are demanding greater compensation for offering credit as losses mount on subprime-mortgage securities and concerns grow that ratings of bond insurers will be cut. Elevated borrowing costs mean the chairman of the Fed, Ben Bernanke, will have to reduce rates further to revive the economy, Fed watchers said.

Banks have been forced to abandon loan sales or offer discounts of as much as 5% for companies including Harrah’s Entertainment Inc., First Data Corp. and Alltel Corp. in the past six months because of investor reluctance to buy debt perceived to be too risky.

General Motors Corp., the world’s largest automaker, said Tuesday it may have to help its former auto-parts unit, Delphi Corp., obtain $6.1 billion in financing to emerge from two years of bankruptcy because of “difficulty” in finding investors for the loans Delphi needs.

“The problem is that every piece of news we’re getting continues to be bad,” a former New York Fed bank research director, and now a professor at Brandeis University in Waltham, Mass., Stephen Cecchetti, said. “They will have to ease more. It’s the only thing they can do.”