SAN FRANCISCO — Mortgage broker Ed Smith Jr. has been arranging home loans for 24 years, and it's never been tougher for him to close a deal than during the past few weeks of turmoil.

As more lenders collapse, the skittish survivors are raising their rates and changing the rules for getting a loan every few hours as they scramble to stay alive. The upheaval has made it virtually impossible to secure financing for scores of borrowers who would have easily qualified for mortgages just a few months ago, creating a lending drought likely to deepen the housing slump.

"You have a ripple effect in the marketplace that is devastating," said Smith, who is based in San Diego.

The fallout figures to be especially hard on homeowners facing dramatically higher payments on exotic mortgages that they obtained two or three years ago. These mortgages began with bargain-basement, or "teaser," interest rates that offered extremely low payments so borrowers could buy a home and refinance later.

But falling home prices and stricter lending criteria have chained these borrowers to their current mortgages, lumping them with higher payments that they can no longer afford.

"I have three borrowers who desperately need to refinance and they aren't going to be able to do it. They are going to lose their homes," said Patrick Schwerdtfeger, a Walnut Creek mortgage broker for Windsor Capital.

Orange County mortgage broker Jack Williams has seen nine mortgage deals unravel in the past 11 days. He has since been able to secure financing for two of the borrowers, but "it doesn't look real promising" for the others as lenders hunker down. "You can have one rate sheet in the morning, then it will change at noon and then it will be completely different again at 5 p.m."

Borrowers with blemished credit records and inadequate paperwork to verify their incomes are having the most trouble getting mortgages.

But the lending crackdown also is affecting more creditworthy borrowers who need to borrow more than $417,000 so they can buy or refinance homes. These so-called "jumbo" loans are common in expensive housing markets like California, where a mid-price home sold for $478,000 in July.

Even borrowers with solid credit are feeling anxious during these uncertain times.

Bridget Hughes, 30, is prepared to put 20 percent down for a townhouse in the Seattle area and appears to have a good enough credit record to secure a $280,000 mortgage. But she still frets that the financing might fall through if there are any unforeseen delays in her application.

"I am nervous," she said yesterday. "When I made an offer on a home, I felt like coming into my office and shouting, 'Look what I am doing!' but decided not to. I am trying not to fall head-over-heels in love with this home in case something goes wrong."