That is the smallest percentage of people eligible for the refinances anywhere in the country, Zillow said.

"The Bay Area is being hit by the fact that it's high-priced, and therefore the loans that were made around the peak years were not conforming (meaning they were above $417,000), and secondly, that (the housing market) has gone into such sharp decline that many homes are underwater by more than 5 percent," said Stan Humphries, vice president of data and analytics for Zillow in Seattle.

A key component of the White House plan calls for assisting homeowners whose home equity has dwindled by letting them refinance into lower-cost mortgages, potentially saving them hundreds of dollars a month and reducing the risk that they may one day lose their homes to foreclosure.

5 percent underwater

But that initiative is only available to people who took out so-called conforming loans of less than $417,000 and whose homes are not more than 5 percent underwater - meaning what they owe is not more than 5 percent greater than their home's value. For instance, someone with a home now worth $300,000 who owes $315,000 could qualify for the refinance - but would be barred if the home's value dropped further.

In the San Francisco metropolitan region - comprising San Francisco, Alameda, Contra Costa, Marin and San Mateo counties - just 8.4 percent of all mortgaged homes meet those criteria, according to Zillow. In the San Jose metropolitan area (Santa Clara County), only 6.9 percent of mortgaged homes would qualify. In Napa County, 8.8 percent of mortgage holders would qualify.

By contrast, more than one-quarter of all U.S. mortgaged homes meet the two basic qualifications for the refinances in terms of mortgage size and the loan-to-value ratio, Zillow said. In some lower-cost areas of the country, such as Memphis, Dayton, Ohio, Fort Collins, Colo., and New Orleans, more than 44 percent of mortgaged homes would qualify, Zillow said.

The Bay Area numbers were higher in two outlying - but much less populated - areas, but still far below the national average. In the Santa Rosa-Petaluma area (Sonoma County) 12 percent of mortgage holders would qualify, according to Zillow, and in Vallejo-Fairfield (Solano County), the number was 17.6 percent. Both areas, especially Vallejo, have suffered a significant foreclosure crisis and seen home values plunge, but they are sufficiently low-cost that presumably more people bought homes with mortgages less than $417,000.

Bottom of the list

Out of 117 metropolitan areas reviewed by Zillow, the Bay Area regions ranked at the bottom in terms of what percentage of mortgages would qualify - behind such pricey areas as Honolulu and New York, and also behind such foreclosure capitals as Stockton, Las Vegas and Florida.

"Around here, most of the market just doesn't qualify; it's going to bypass us," said James Wilcox, a professor of finance at the Haas School of Business at UC Berkeley.

The program is designed for people who are still current on their mortgage payments but have seen their home values sink, which makes it more difficult to get a regular refinance because they don't have enough equity. The administration said the plan would help 4 million to 5 million families to potentially save thousands of dollars a year on mortgage payments.

"Households that can have their monthly payments reduced by those kinds of amounts will be helped considerably," Wilcox said. "For folks who still have their jobs, this puts a lot more cash in their pockets. Presumably, that will help spending around the economy generally. In the households that have lost a paycheck and were close to the edge, for some folks it will make the difference" between losing or keeping their homes.

But Tom Davidoff, also a professor at Haas, said the refinances, with their emphasis on helping "responsible homeowners," meaning people who made a down payment and have made mortgage payments on time, "is a political sop to say we're doing something for people who aren't in big trouble."

"It doesn't surprise me that we'd be getting the least benefit of the refis in the country," he said.

Wider assistance

The Obama plan's other major foreclosure-prevention initiative, a $75 billion program to encourage lenders to modify loans for struggling homeowners, including both those behind on their payments and ones who are still current, would apply as broadly in the Bay Area as anywhere else, experts said. And the White House plan to inject an additional $200 billion into Fannie Mae and Freddie Mac would also be a positive here by helping to make mortgages cheaper and more widely available.

And overall, many market analysts said, the plan still has local benefit in that anything that boosts housing boosts the Bay Area, too.

"Honestly, I think it's still good," Davidoff said. "Anything we do to avoid foreclosures and strengthen the housing market is a good thing for the Bay Area because we don't want a national depression."

E-mail Carolyn Said at csaid@sfchronicle.com.

This article appeared on page A - 1 of the San Francisco Chronicle