WASHINGTON — More than 350,000 families made homeless by Hurricane Katrina would get emergency housing vouchers averaging $600 a month for up to six months under a measure approved Wednesday by the Senate.

Any displaced family regardless of income would be eligible for the program, expected to cost $3.5 billion over six months.

The action came as Senate Democrats scolded the nation's security chief for failing to take advantage of a national emergency response plan to send massive federal aid to the Gulf Coast before Hurricane Katrina hit.

Democrats said Homeland Security Secretary Michael Chertoff delayed declaring Katrina an "incident of national significance" — a designation that would have triggered a quick and massive federal response — until a day after the hurricane hit, even though weather forecasts predicted the storm would cause widespread destruction.

A Chertoff spokesman denied the charge, pointing to millions of ready-made meals, thousands of blankets and dozens of federal rescue teams sent to the region as the hurricane approached.

The housing measure, by Sen. Paul Sarbanes, D-Md., was attached on a voice vote to an unrelated spending bill covering the Commerce and Housing and Urban Development departments. The Senate was to pass the overall bill Thursday; a final version needs to be worked out with the House, which approved a similar spending bill for the two departments in June.

"Any person or family displaced as a result of Hurricane Katrina . . . could get a temporary housing voucher. This is without regard to their income situation," Sarbanes said. "It recognizes the storm hit rich and poor alike, and this is an effort to give them some immediate, short-term help so they can move out of the situation in which they find themselves."

The Bush administration also acted on Wednesday to begin covering medical costs for low-income refugees from the worst natural disaster in U.S. history.

The Centers for Medicare and Medicaid Services planned to announce on Thursday that it will pick up all costs of Medicaid care for an low-income evacuees who fled to Texas. The state's senior senator, Republican Kay Bailey Hutchison, received a phone call late Wednesday from CMS Administrator Mark McClellan about the forthcoming aid, said her spokesman, Chris Paulitz.

An estimated 250,000 refugees from the flooding, an overwhelming majority of them believed to be qualified for Medicaid, are now in Texas. For five months state matching funds that are part of the Medicaid program will be waived, said Paulitz.

He quoted McClellan as saying the administration is looking at the Texas waivers as a possible model for other states.