PENSACOLA, Fla. (AP) - President Barack Obama is capping two

days in the suffering Gulf of Mexico with a solemn, high-stakes

address to the nation that will lay out the enormous effort needed

to right the multifaceted damage from the country's worst

environmental disaster.

With the political import of Tuesday evening's address clear,

Obama for the first time will use the Oval Office as an austere

backdrop for a speech in which he will assign himself and his

administration the momentous task of bringing back the Gulf's

teeming wildlife and beauty to what it was before it was fouled by

hundreds of millions of gallons of oil.

To victims of the spill, those who've lost their loved ones or

livelihood or who've been less directly impacted, Obama will

promise that their injuries will be addressed through a

compensation fund he's directing BP PLC to establish.

To the residents of the Gulf and the nation as a whole, Obama

will make a commitment to deliver an ecological and economic

restoration that will define his presidency as surely as George W.

Bush's failure to make good on his promises on Hurricane Katrina

defined Obama's predecessor's.

Obama will even make a promise to future generations by using

the speech to push Congress for action on sweeping energy and

climate legislation that could leave his imprint on the nation's

energy policy for decades to come.

Obama's address to the nation sets the stage for his showdown

White House meeting Wednesday with top executives at British-based

BP, the company that leased the rig that exploded April 20 and led

to the leak of millions of gallons of coast-devastating crude. It's

part of an effort by Obama, who's been accused of appearing

somewhat detached as the oil spill disaster has unfolded, to

convince a frightened Gulf Coast and a skeptical nation that he is

in command.

It was Obama himself who decided to use the Oval Office for the

speech, according to White House spokesman Bill Burton, because of

the urgency of the task ahead.

"What we're seeing in the Gulf is a catastrophe the likes of

which our country has never seen before," Burton said of the

president's thinking. "And so talking directly with the American

people about what we're doing to address this crisis and what we're

going to be doing moving forward is very important to the president

right now."

Obama was to deliver the speech upon his return from a two-day

swing through Mississippi, Alabama and Florida, his fourth trip to

the Gulf since the Deepwater Horizon drilling rig explosion that

set off the disaster, but his first outside the hardest-hit state

of Louisiana.

The trip gave him ammunition for the speech and for his meeting

with BP executives where he intends to finalize the details of a

victims compensation fund. He visited vacant beaches in Mississippi

where the threat of oil had scared off tourists, heard the stories

of local employers losing business, watched hazmat-suited workers

scrub down boom in a staging facility in Theodore, Ala., and took a

ferry ride through Mobile Bay and then to Orange Beach, Ala., where

oil has lapped on the shore.

He was beginning the day Tuesday in Pensacola, Fla., where he

was to attend a briefing and then make remarks at Naval Air Station

Pensacola.

"We're gathering up facts, stories right now so that we have an

absolutely clear understanding about how we can best present to BP

the need to make sure that individuals and businesses are dealt

with in a fair manner and a prompt manner," the president said

Monday.

"I am confident that we're going to be able to leave the Gulf

Coast in better shape than it was before," he said.

That pledge was reminiscent of George W. Bush's promise to

rebuild the region "even better and stronger" than before

Hurricane Katrina in 2005. Bush could not make good on that

promise, and Obama did not spell out how he would fulfill his.

Tuesday's speech will give him the chance.

Presidents reserve the Oval Office for rare televised addresses.

When they take their place behind the desk, it's a time for

solemnity and straight talk - often a moment of history. There is a

sense of gravity. One man by himself before one television camera

speaking to the nation.

Oval Office addresses typically aren't lengthy discourses like a

State of the Union, but if a president has to go for broke, this is

where he does it. Bush addressed the nation from the Oval on the

evening of Sept. 11, 2001. Ronald Reagan spoke there after the

space shuttle Challenger explosion. John F. Kennedy grimly

explained the Cuban missile crisis. Richard Nixon announced his

resignation.

Obama hasn't used it yet. Not even during the worst economic

crisis since the Great Depression. Not to explain painfully high

unemployment rates. Or bank and auto company bailouts. Not to speak

of terrorism threats. Even when his health insurance plan was in

peril, he did not speak from the Oval Office to rally support or

explain to Americans why he considered it vital.