Updated

Republican White House hopeful John McCain announced his candidacy for the 2008 presidential race in New Hampshire on Wednesday.

"Today, I announce my candidacy for president of the United States," McCain told supporters in Portsmouth, N.H. "I do so grateful for the privileges this country has already given me; mindful that I must seek this responsibility for reasons greater than my self-interest; and determined to use every lesson I've learned through hard experience and the history I've witnessed, every inspiration I've drawn from the patriots I've known and the faith that guides me to meet the challenges of our time."

McCain, 70, if elected, would enter the White House as the oldest first-term president.

"I'm not the youngest candidate. But I am the most experienced," McCain said, an ex-Navy pilot and former Vietnam War captive. "I know how to work with leaders who share our dreams of a freer, safer and more prosperous world, and how to stand up to those who don't. I know how to fight and how to make peace. I know who I am and what I want to do."

The announcement is the official launch of McCain's second presidential campaign, though he has been in the race longest, forming his exploratory committee back in November. The senator lost his first attempt for the Republican nomination to President Bush seven years ago.

"When I'm president I'll offer common sense, conservative and comprehensive solutions to these challenges," McCain is to say. "Congress will have other ideas, and I'll listen to them. I'll work with anyone who is serious and sincere about solving these problems."

Click here for more coverage in FOXNews.com's You Decide 2008 center.

He also said he wants to focus on cutting back on America's dependence on foreign oil.

"Our dependence on foreign sources of energy not only harms our environment and economy, it the world where our values aren't shared and our interests aren't a priority," he said.

McCain has been the most vocal supporter of continuing action in Iraq. He has made several trips there and repeatedly has said the best way to win is to increase troop levels.

"We are fighting a war in two countries, and we're in a global struggle with violent extremists who despise us, our values and modernity itself," McCain said. "If we are to succeed, we must rethink and rebuild the structure and mission of our military; the capabilities of our intelligence and law enforcement agencies; the purposes of our alliances; the reach and scope of our diplomacy; the capacity of all branches of government to defend us."

McCain's plans have been in the works for months, as he has made campaign stops in Iowa, New Hampshire and South Carolina.

McCain started his pre-campaign as the likely front-runner for the GOP nomination at year's end. He is now trailing former New York City Mayor Rudy Giuliani in national polls and ex-Gov. Mitt Romney of Massachusetts in money raised.

For his formal announcement, McCain returns to New Hampshire, the state that gave him an 18-percentage-point upset over Bush in the 2000 primary.

FOX News' Aaron Bruns and The Associated Press contributed to this report.