U.S. apartment rents fell in the fourth quarter from the third as the national vacancy rate climbed to a four-year high of 6.6 percent, according to a report just published by Reis Inc., a New York-based research firm.The report defies the expectation that apartments would benefit from the housing slump as job losses and lower wages are cutting into the pool of potential renters in their twenties and thirties.

Asking rents fell 0.1 percent from the previous quarter, to $1,052 on average, their first quarter-to-quarter decline in almost six years. Effective rents, what tenants actually paid, fell to an average $996 last quarter, down 0.4 percent from the prior quarter.Vacancy Rate

The vacancy rate rose to 6.6 percent in the fourth quarter from 6.2 percent in the third quarter and 5.7 percent at the end of 2007. The fourth quarter matched the vacancy rate in 2005’s first quarter and was the highest since the fourth quarter of 2004, when it was 6.7 percent, according to Reis.

Vacancies increased in 66 of the 79 cities measured by Reis and effective rents fell in 54 markets.

The net change in occupied space, a measure of leasing known as absorption, shrank by 13,283 units.

In a report Thursday, the Center for Responsible Lending, a nonpartisan research firm, called on lenders to modify mortgage terms for subprime borrowers, saying the financial damage caused by subprime lending will fester without modifications.

The organization pointed out that 1.5 million families have lost their homes and another 2 million families are facing that fate.

“Because the foreclosure crisis is at the root of this recession, the continuing flood of foreclosures stymies any chance of real economic recovery,” says Center for Responsible Lending president Michael Calhoun. “Any economic stimulus would be a Band-aid solution unless we stop the hemorrhaging in our housing market.”

In its report, the group urges the Treasury to require recipients of funds from the governments’s Troubled Assets Relief Program to adopt streamlined modification programs and also guarantee sustainably modified mortgages against default.

The Center also says Congress should act fast to lift the ban on judicial loan modifications, which would prevent hundreds of thousands of foreclosures without requiring any taxpayer funding.