WASHINGTON  - About 20 percent of struggling U.S. homeowners eligible for loan workouts have entered into a trial modification, but it is unclear how many of them will be able to keep the lower payments permanently, the Treasury Department said on Tuesday.

It said there were 650,994 active trial modifications through October under President Barack Obama's plan to help the housing market. That was up from 487,081, or 16 percent, participating through September.

The Treasury did not release figures for trial modifications that have been made permanent.

Most loan modifications result in lower monthly payments, although some lead to reduced principal on mortgages. Trial modifications were initially for three months, but the Treasury added 60 days, effectively making them last five months.

Borrowers need to submit more detailed documentation to make a loan modification permanent.

Under pressure from Congress, the Treasury released state-by-state details of the loan modifications.

As this report demonstrates, struggling homeowners in every state now benefit from reduced monthly mortgage payments and have an opportunity to stay in their homes, said Michael Barr, Treasury assistant secretary for financial institutions.

California and Florida topped the list of modifications, with 134,609 and 82,614 respectively. Half a dozen states, all sparsely populated, had fewer than a 1,000 modifications. North Dakota had just 170.

The Treasury did not include the conversion rate to permanent loans, which experts say is the key to determining the program's real success or failure. Those figures are expected later this month, a Treasury spokeswoman said.

Herb Allison, the Treasury's assistant secretary for financial stability, said last month that fewer than 10,000 trial modifications had been made permanent.

The report comes as new data from the National Association of Realtors showed house prices continued to fall in 4 out of 5 U.S. cities in the third quarter compared with a year ago.

The Treasury said that Saxon Mortgage Services had the highest percentage of trial modifications, at 44 percent of those eligible.

Two servicers, Bank United and Franklin Credit Management Corporation, had not extended any modification offers. MorEquity Inc had just three active modifications through October, statistically zero percent of its 2,299 eligible borrowers.

Bank of America, JP Morgan Chase and Wells Fargo were the top three servicers with 136,994, 133,988 and 93,652 active trial modifications, respectively. But Bank of America's percentage of eligible borrowers was the lowest of the big banks -- just 14 percent of eligible borrowers.

Citigroup had the highest participation of the big banks, with 88,968 active load modifications, or 40 percent of its eligible borrowers. JP Morgan's percentage was 32 percent, while Wells Fargo came in at 29 percent.

The monthly report comes as pressure mounts on the administration to do more to make sure trial modifications are turned into permanent modifications.

A congressional watchdog said last month that government programs to fight the foreclosure crisis are inadequate and should be reworked, expanded and supplemented with new ideas.

(Reporting by Corbett B. Daly; Editing by Dan Grebler)