WASHINGTON — More than 350,000 families left homeless by Hurricane Katrina would receive emergency-housing vouchers averaging $600 a month for up to six months under a measure approved yesterday 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 Senate yesterday also rejected by a 55-44 vote a Democratic proposal to establish an independent, bipartisan commission — similar to one enacted after the Sept. 11 terrorist attacks — to examine what went wrong in Katrina's wake. Sens. Patty Murray and Maria Cantwell, D-Wash., voted in favor of the panel.

The votes on housing and an independent commission 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 one 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 readymade 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 today; a final version needs to be worked out with the House.

The Senate also planned today to debate a plan expected to cost between $5 billion and $7 billion to speed health care for people displaced by Katrina. The measure would ease rules for the Medicaid federal health-care program.

Also today, Congress hoped to work through a bill that would waive penalties for hurricane victims who tap their 401(k) retirement-savings accounts and would allow a tax deduction to anyone who houses evacuees for two months or more.