WASHINGTON -- Moving to blunt criticism that his administration has been slow in reacting to the largest U.S. crude oil spill in decades, President Barack Obama has dispatched two of his Cabinet members to make the rounds of the Sunday talk shows.

Later Sunday, Obama was to fly to Louisiana for a visit to the Gulf Coast and a firsthand update on the massive spill that threatens to bring catastrophic environmental and economic damage in its wake.

The underwater spill remained unstopped and impossible to measure, raising fears it could be pouring more oil into the Gulf than earlier believed. The Coast Guard estimated that at least 1.6 million gallons of oil have spilled since the April 20 explosion that killed 11 workers on an offshore rig. In the Exxon Valdez disaster, an oil tanker spilled 11 million gallons off Alaska's shores in 1989.

Obama has said his administration will do all that it can to battle the spill, which came from a BP oil company exploratory rig. The spill is already the worst in U.S. waters in decades.

Obama has relied on reports from agency chiefs and Coast Guard officials since the magnitude of the spill became clear late Wednesday. Aides report he's been getting regular updates.

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Interior Secretary Ken Salazar and Homeland Security Secretary Janet Napolitano scheduled appearances across the Sunday morning talk shows to detail the administration's efforts in dealing with the environmental disaster. Joining them was the commandant of the Coast Guard, Adm. Thad Allen.

Obama has said no new offshore oil drilling leases will be issued unless rigs have new safeguards to prevent a repeat of the explosion that unleashed the massive spill.

The spill came just weeks after Obama announced plans to open up large areas of the Eastern Seaboard and a part of the Gulf for possible future oil drilling. And it's led to increasing calls to reconsider that initiative by environmentalists and coastal state lawmakers.