ASHINGTON, Sept. 20 — President Bush tonight chose Governor Tom Ridge of Pennsylvania, a longtime friend and political ally and a combat veteran, to head a new Office of Homeland Security.

Governor Ridge, a highly popular Republican governor, was one of Mr. Bush's leading candidates to be his running mate last year and is viewed as an ascendant leader in the party's moderate wing.

Mr. Bush, who met Governor Ridge more than two decades ago when they worked on George Bush's 1980 campaign for president, praised him tonight as "a true patriot and a trusted friend."

The president said Governor Ridge would receive cabinet-level status and be "reporting directly to me," as he seeks to coordinate the myriad intelligence, defense and law enforcement agencies involved in identifying and thwarting terrorist activities against domestic targets.

"He will lead, oversee and coordinate a comprehensive national strategy to safeguard our country against terrorism and respond to any attacks that may come," Mr. Bush said.

Governor Ridge, 56, brings several assets to the task. In addition to his close ties to the president, he is a Vietnam veteran who earned the Bronze Star for Valor, a Harvard graduate with a flair for plain speaking and a politician who has spent a good part of his career battling crime.

A spokesman for Governor Ridge said that he would resign his post effective Oct. 5 and that Lt. Gov. Mark S. Schweiker, a fellow Republican, would finish the term, which ends in January 2003. Tim Reeves, the governor's press secretary, said Mr. Ridge had been approached by the president late Wednesday and again on Thursday morning and decided to take the job after previously saying he was not interested in any administration posts.

"Things have changed and the world is different," Mr. Reeves said. "This was a request from his president that he could not say no to."

Reared in a working-class family in Erie, Pa., Mr. Ridge grew up in veterans' public housing and won a scholarship to college, graduating with honors in 1967. He was drafted into the Army and saw combat as a staff sergeant in Vietnam.

After he finished law school and worked briefly for the elder Mr. Bush's campaign, Mr. Ridge was narrowly elected to the House. His voting record there confounded analysts by defying an easy label. He was liberal on some social issues and traditional on others; the blend of views played well with his constituents, who re-elected him by wide margins five times.

In 1994, Mr. Ridge ran for governor, calling for tougher action against crime and an easing of taxes and regulation for business. Once in office, Governor Ridge became known as a fiscal conservative, cutting state spending in half, while pushing tax cuts year after year, in a crusade that he says has saved residents $4 billion.

Mr. Ridge has been a firm supporter of the death penalty and has signed execution warrants as governor.

That record, coupled with Governor Ridge's advocacy of vouchers for private schools and a welfare overhaul, prompted many Bush supporters to see him as an ideal choice for vice president. But Mr. Ridge ran afoul of conservatives for his support of abortion rights and his opposition in the House to the Strategic Defense Initiative and the MX missile.

Governor Ridge's critics said the two-term governor had jilted public education, built lavish sports stadiums and been overly accommodating to corporate interests.

In Pennsylvania last week, the governor met with relatives of those who died aboard United Airlines Flight 93, apparently after waging a struggle with hijackers.

"They saved hundreds, perhaps thousands of lives," he told weeping relatives. "Thank God for their lives, their families and their heroism."