WASHINGTON — The Obama administration is proposing to open vast expanses of water along the Atlantic coastline, the eastern Gulf of Mexico and the north coast of Alaska to oil and natural gas drilling, much of it for the first time, officials said Tuesday.

The proposal — a compromise that will please oil companies and domestic drilling advocates but anger some residents of affected states and many environmental organizations — would end a longstanding moratorium on oil exploration along the East Coast from the northern tip of Delaware to the central coast of Florida, covering 167 million acres of ocean.

Under the plan, the coastline from New Jersey northward would remain closed to all oil and gas activity. So would the Pacific Coast, from Mexico to the Canadian border.

The environmentally sensitive Bristol Bay in southwestern Alaska would be protected and no drilling would be allowed under the plan, officials said. But large tracts in the Chukchi Sea and Beaufort Sea in the Arctic Ocean north of Alaska — nearly 130 million acres — would be eligible for exploration and drilling after extensive studies.

The proposal is to be announced by President Obama and Interior Secretary Ken Salazar at Andrews Air Force Base in Maryland on Wednesday, but administration officials agreed to preview the details on the condition that they not be identified.

The proposal is intended to reduce dependence on oil imports, generate revenue from the sale of offshore leases and help win political support for comprehensive energy and climate legislation.

But while Mr. Obama has staked out middle ground on other environmental matters — supporting nuclear power, for example — the sheer breadth of the offshore drilling decision will take some of his supporters aback. And it is no sure thing that it will win support for a climate bill from undecided senators close to the oil industry, like Lisa Murkowski, Republican of Alaska, or Mary L. Landrieu, Democrat of Louisiana.

The Senate is expected to take up a climate bill in the next few weeks — the last chance to enact such legislation before midterm election concerns take over. Mr. Obama and his allies in the Senate have already made significant concessions on coal and nuclear power to try to win votes from Republicans and moderate Democrats. The new plan now grants one of the biggest items on the oil industry’s wish list — access to vast areas of the Outer Continental Shelf for drilling.

But even as Mr. Obama curries favors with pro-drilling interests, he risks a backlash from some coastal governors, senators and environmental advocates, who say that the relatively small amounts of oil to be gained in the offshore areas are not worth the environmental risks.

The Obama administration’s plan adopts some drilling proposals floated by President George W. Bush near the end of his tenure, including opening much of the Atlantic and Arctic Coasts. Those proposals were challenged in court on environmental grounds and set aside by President Obama shortly after he took office.

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

Actual drilling in much of the newly opened areas, if it takes place, would not begin for years.

Mr. Obama said several times during his presidential campaign that he supported expanded offshore drilling. He noted in his State of the Union address in January that weaning the country from imported oil would require “tough decisions about opening new offshore areas for oil and gas development.”

Perhaps in anticipation of controversy, the new policy has been closely held within the administration. White House and Interior Department officials began briefing members of Congress and local officials in affected states late Tuesday.

It is not known how much potential fuel lies in the areas opened to exploration, although according to Interior Department estimates there could be as much as a three-year supply of recoverable oil and more than two years’ worth of natural gas, at current rates of consumption. But those estimates are based on seismic data that is, in some cases, more than 30 years old.

The first lease sale off the coast of Virginia could occur as early as next year in a triangular tract 50 miles off the coast that had already been approved for development but was held up by a court challenge and additional Interior Department review, officials said.

But as a result of the Obama decision, the Interior Department will spend several years conducting geologic and environmental studies along the rest of the southern and central Atlantic Seaboard. If a tract is deemed suitable for development, it is listed for sale in a competitive bidding system. The next lease sales — if any are authorized by the Interior Department — would not be held before 2012.

The eastern Gulf of Mexico tract that would be offered for lease is adjacent to an area that already contains thousands of wells and hundreds of drilling platforms. 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.

Drilling there has been strongly opposed by officials from both political parties in Alabama and Florida who fear damage to coastlines, fisheries, popular beaches and wildlife. Interior Department officials said no wells would be allowed within 125 miles of the Florida and Alabama coasts, making them invisible from shore.

The Interior Department and the Pentagon are discussing possible restrictions on oil and gas operations in some areas off Virginia and Florida, home to some of the nation’s biggest Navy and Air Force facilities. States are also likely to claim rights to the revenues from oil and gas deposits within 3 to 12 miles of shore and to some portion of lease proceeds, officials said.

Mr. 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.

In many of the newly opened areas, drilling would begin only after the completion of geologic studies, environmental impact statements, court challenges and public lease sales. Much of the oil and gas may not be recoverable at current prices and may be prohibitively expensive even if oil prices spike as they did in the summer of 2008.

At the Wednesday event, Mr. Obama is also expected to announce two other initiatives to reduce oil imports, an agreement between the Pentagon and the Agriculture Department to use more biofuels in military vehicles and the purchase of thousands of hybrid vehicles for the federal motor pool.