President Obama’s proposal to open vast expanses of American coastlines to oil and natural gas drilling drew criticism from both sides in the drilling debate.

Interior Secretary Ken Salazar developed the offshore drilling plan after conducting four public meetings over the past year in Alaska, California, Louisiana and New Jersey. The Interior Department received more than 500,000 public comments on the issue. Mr. Salazar has said that he hoped to rebalance the nation’s oil and gas policy to find a middle ground between the “drill here drill now” advocacy of many oil industry advocates and the preservationist impulse to block oil exploration beneath virtually all public lands and waters. He has called the offshore drilling plan a new chapter in the nation’s search for a comprehensive energy policy that can open new areas to oil and gas development “in the right way and in the right places,” according to an aide.

The eastern Gulf area is believed to contain as much as 3.5 billion barrels of oil and 17 trillion cubic feet of gas, the richest single tract that would be open to drilling under the Obama plan.

Mr. Obama said several times during his presidential campaign that he supported expanded offshore drilling.

Mr. Obama’s proposal would put Bristol Bay, home to major Alaskan commercial fisheries and populations of endangered whales, off limits to oil rigs.

he said, “and that for the sake of the planet and our energy independence, we need to begin the transition to cleaner fuels now.”

Mr. Obama also tried to answer oil industry officials and Republicans in Congress who would claim that the president did not go far enough. “They’d deny the fact that with less than 2 percent of oil reserves, but more than 20 percent of world consumption, drilling alone cannot come close to meeting our long-term energy needs,”

Mr. Obama said in his remarks: “There will be those who strongly disagree with this decision, including those who say we should not open any new areas to drilling, But what I want to emphasize is that this announcement is part of a broader strategy that will move us from an economy that runs on fossil fuels and foreign oil to one that relies more on homegrown fuels and clean energy. And the only way this transition will succeed is if it strengthens our economy in the short term and long term. To fail to recognize this reality would be a mistake.”

The environmentally sensitive Bristol Bay in southwestern Alaska would be protected and no drilling would be allowed under the plan, officials said.