The federal government’s plan to streamline modifications of troubled loans held by Fannie Mae and Freddie Mac won’t help the majority of people threatened with foreclosure, CNNMoney.com said.

Under a plan unveiled Tuesday, homeowners whose loans are owned or backed by the two companies and who are at least 90 days behind can enter a streamlined modification program. Their payments would be adjusted through lower interest rates or longer repayment terms that would total no more than 38 percent of their monthly household income. In some cases, payment on part of the loans’ principal may be deferred, though not reduced.

The interest rate could be lowered to as little as 3 percent for five years. After that, it would increase by 1 percentage point a year until it hits either the market rate or the original interest rate, whichever is lower, officials said.

Unlike previous federal efforts, participation by loan servicers is not voluntary. They will now work with eligible borrowers to set more affordable mortgage payments, using the guidelines laid out Tuesday.

The program could help more than 400,000 homeowners.

Though financial experts and some government officials called the plan a positive step forward, they said much more needs to be done to handle the mortgage crisis. The program does not address the heart of the problem — troubled loans held by private investors.

Though Fannie Mae and Freddie Mac own or guarantee 58 percent of all mortgages on single-family homes, these loans represent only 20 percent of serious delinquencies. The majority of the problem mortgages were bundled into securities, which were sold in pieces to investors.

“This is a step in the right direction but falls short of what is needed to achieve wide-scale modifications of distressed mortgages, particularly those held in private securitization trusts,” said Federal Deposit Insurance Corp. Chairwoman Sheila Bair, who has proposed an alternate plan addressing securitized loans. “As we lend and invest hundreds of billions of dollars to help institutions suffering leveraged losses from defaulting mortgages, we must also devote some of that money to fixing the front-end problem: too many unaffordable home loans.”

To broaden existing foreclosure fixes, Bair supports using up to $50 billion of the $700 billion financial sector rescue plan to guarantee modified loans. This would give servicers an incentive to adjust the loan terms and could help up to 3 million homeowners, though the number is not firm.

Problems in the mortgage market remain concentrated in the subprime loans, which are mainly held by investors who have resisted modifying the loan terms.