OKLAHOMA CITY — Oklahoma House Speaker T.W. Shannon resigned Tuesday from one of the most powerful positions in state government to focus on his run for a U.S. Senate seat and kicked into overdrive a behind-the-scenes race to succeed him.

Shannon said on the House floor that he would resign as speaker immediately, telling his 100 colleagues it wouldn't be fair to continue in the post while running a statewide campaign for higher office.

"I want to do the right thing, so I am today stepping down," Shannon said in a 10-minute speech from the front of the chamber. "It has been the honor of a lifetime to serve alongside of you and to have your trust as speaker of the House."

The speaker's announcement was delayed for nearly 30 minutes while legislators bickered over, then passed, a resolution requiring the Pledge of Allegiance to be said each day on the House floor.

"I joke that if God were to give me but four months to live, I'd want to spend them here because they're the longest four months of my life every single year," Shannon said.

Shannon's resignation will formalize the race within the 72-member Republican caucus to replace him among Reps. Jeff Hickman of Dacoma, Mike Jackson of Enid, and Jason Nelson of Oklahoma City. All three confirmed to The Associated Press that they are actively seeking the post, and each said he does not expect the race to divide the caucus.

"The three people I know of who have expressed an interest in this position are all friends, and it's going to be a short process, and I think everyone is more than capable enough of working together," Hickman said.

A secret-ballot election will be held Monday in the closed-door caucus meeting, and potential candidates have until the end of this week to formally file for the speaker's post, said Rep. Weldon Watson, R-Tulsa and caucus chairman.

"Five days is about as fast as you can do it," Watson said.

Jackson is speaker pro tempore, the No. 2 position in the House, and rules provide for him to serve as speaker until an election is held.

The speaker not only oversees the House's roughly 115 employees and $16 million annual budget, but also appoints members and chairmen of various committees and represents the chamber in negotiations with the governor and Senate on policy and budget.

Jackson said he doesn't intend to make any major changes to the House committee structure or operations, even if elected speaker.

"I think it would be a mistake to make any changes like that," Jackson said.

House Democratic Leader Rep. Scott Inman said that while electing a coalition speaker with the help of the chamber's 29 Democrats is "a longshot," he isn't entirely ruling out the possibility.

"I think my caucus would certainly take a look at that," Inman said.

Shannon is a 35-year-old Republican from Lawton who announced last week that he would run for the U.S. Senate seat being vacated at the end of the year by Sen. Tom Coburn. Shannon will face two-term U.S. Rep. James Lankford and at least two other Republicans in the GOP primary.

First elected to his Oklahoma House seat in Lawton in 2006, Shannon, a member of the Chickasaw Nation, was both the youngest and first African-American speaker of the House when he was formally elected at the start of the 2013 legislative session.

Shannon touted some of the conservative policies he and his GOP colleagues have approved during his seven years in office, including cuts to the state's income tax, changes to the workers' compensation and anti-abortion legislation.

Shannon will continue to represent his House District 62 seat in west Lawton for the remainder of his term.