WASHINGTON – Former House Speaker Newt Gingrich will not run for president in 2008 after determining he could not legally explore a bid and remain as head of his tax-exempt political organization, a spokesman said Saturday.

“Newt is not running,” spokesman Rick Tyler said. “It is legally impermissible for him to continue on as chairman of American Solutions (for Winning the Future) and to explore a campaign for president.”

Mr. Gingrich decided “to continue on raising the challenges America faces and finding solutions to those challenges” as the group’s chairman, Mr. Tyler said, “rather than pursuing the presidency.”

Over the past few months, Mr. Gingrich had stoked speculation he might enter the crowded GOP field. He noted that Republicans, especially conservatives, were unhappy with the candidates already in the race.

Yet he also has spoken positively of all the leading contenders, including Mayor Giuliani, Mitt Romney, the former governor of Massachusetts, Fred Thompson, the former Senator of Tennessee Sen. Fred Thompson and Senator McCain of Arizona.

Just last week, Mr. Gingrich said he had given himself a deadline of Oct. 21 to raise $30 million in pledges for a possible White House bid, acknowledging the task was difficult but not impossible.

He abruptly dropped the idea today, apparently unwilling to give up the chairmanship of American Solutions, the political arm of Mr. Gingrich’s lucrative empire as an author, pundit and consultant.

American Solutions, a tax-exempt committee he started last October, has paid for Mr. Gingrich’s travel and has a pollster and fundraiser on staff.

Mr. Gingrich makes hundreds of speeches each year, many paid. He will not say how much he charges, and neither will the Washington Speakers Bureau, which books him. But some clients have said they paid $40,000 for a speech.

He also has a contract with Fox News for commentaries and specials; Fox said it does not disclose the terms of its contracts. Mr. Gingrich also is a senior fellow at the conservative American Enterprise Institute.

Mr. Gingrich has a daily radio broadcast on more than 400 stations, and he writes a free online newsletter with 200,000 subscribers that is distributed by the conservative news magazine Human Events.

He also has a for-profit think tank, the Center for Health Transformation, which grew out of the consulting firm he started after leaving Congress in 1999.

Mr. Gingrich quit Congress when his party, after spotlighting President Clinton’s affair with Monica Lewinsky, lost seats in the 1998 elections. The next year, Mr. Gingrich’s involvement with a congressional aide, Callista Bisek, led to his divorce from his second wife, Marianne; he later married Bisek.

Mr. Gingrich, 64, tried to rehabilitate his image this year by admitting publicly to his extramarital affair during the Clinton impeachment scandal. He made the admission in an interview last month with Focus on the Family founder James Dobson, and he won praise for the acknowledgment from another conservative Christian leader, the Rev. Jerry Falwell.