(Adds quotes from Tillerson)
* Tillerson had been asked to resign on Friday
* Trump wanted new team in place for proposed North Korea talks
* Latest high-level departure from White House team
By Roberta Rampton and Lesley Wroughton
WASHINGTON, March 13 (Reuters) - U.S. President Donald Trump fired Secretary of State Rex Tillerson on Tuesday after a series of public rifts over policy on North Korea, Russia and Iran, replacing his chief diplomat with loyalist CIA Director Mike Pompeo.
The biggest shakeup of Trump's Cabinet since he took office in January 2017 was announced by the president on Twitter as his administration works toward a meeting with North Korea's leader.
The rare firing of the United States' top diplomat capped months of friction between the Republican president and the 65-year-old former Exxon Mobil Corp chief executive. The tensions peaked last fall amid reports Tillerson had called Trump a "moron" and considered resigning. Tillerson never denied using the word.
Some foreign policy experts expressed dismay at the decision to swap out top diplomats so soon before the unprecedented meeting and worried that Pompeo would encourage Trump to scrap the Iran nuclear deal and be hawkish on North Korea.
Critics said the move would sow more instability in the volatile Trump administration and marks the departure of another moderate who sought to emphasize the United States' strong ties to its allies amid Trump's criticism. Last week, top economic adviser Gary Cohn quit after Trump announced trade tariffs that would affect U.S. allies.
Trump announced the changes in a morning Twitter post and later told reporters more about why he removed Tillerson.
"We got along actually quite well but we disagreed on things," Trump said. "When you look at the Iran deal: I think it's terrible, I guess he thinks it was OK. I wanted to break it or do something, and he felt a little bit differently."
Later at the State Department, a visibly emotional Tillerson said Trump called him around noon from Air Force One and that he had also spoken with White House Chief of Staff John Kelly.
He said his tenure ends on March 31 but he would delegate his responsibilities to John Sullivan, deputy secretary of state, at the end of Tuesday.
"What is most important is to ensure an orderly and smooth transition during a time that the country continues to face significant policy and national security challenges," Tillerson, whose voice quivered at times, told reporters in a packed briefing room.
Tillerson had developed a strong relationship with Secretary of Defense Jim Mattis, and the two were seen as a moderating influence on some of Trump's policies.
"I'm told for the first time in most people's memory the Department of State and the Department of Defense have a close working relationship where we all agree the U.S. leadership starts with diplomacy," he said.
In contrast, Trump said he and Pompeo have "a similar thought process."
Pompeo, a former Army officer who represented a Kansas district in the House of Representatives before taking the CIA job, is seen as a Trump loyalist who has enjoyed a less hostile relationship with career spies than Tillerson had with career diplomats.
Trump chose the Central Intelligence Agency's deputy director, Gina Haspel, to replace Pompeo at the CIA. A veteran CIA clandestine officer, Haspel is backed by many in the U.S. intelligence community but is regarded warily by some in Congress for her involvement in the agency's "black site" detention facilities.
Senior White House officials said Trump wanted his new team in place before any summit with Kim Jong Un, who invited the U.S. president to meet by May after months of escalating tensions over North Korea's nuclear and missile programs.
TILLERSON UNCLEAR ON REASON
Tillerson's imminent departure had been rumored for several months, and Trump said he and Tillerson had discussed the move. State Department officials said Tillerson did not know why he was being pushed out and had intended to stay. One of them was fired later on Tuesday.
Foreign policy experts from Republican and Democratic administrations also questioned Trump's timing and choice, noting that Pompeo was known as a political partisan who strongly opposed the 2015 Iran nuclear deal.
Evans Revere, a former senior U.S. diplomat who dealt with North Korea under President George W. Bush, said Trump's move sends "a bad signal about the role of diplomacy."
"Tillerson's replacement by ... Pompeo, who is known as a political partisan and an opponent of the Iran agreement, raises the prospect of the collapse of that deal, and increases the possibility that the administration might soon face not one, but two nuclear crises," he said.
Senior White House officials said Chief of Staff Kelly had asked Tillerson to step down on Friday but did not want to make it public while he was on a trip to Africa. Trump's Twitter announcement came only a few hours after Tillerson landed in Washington.
Tillerson appeared to be caught by surprise last week when Trump announced he had accepted Kim's invitation to meet and the secretary of state cut short his trip.
"Mike Pompeo, Director of the CIA, will become our new Secretary of State. He will do a fantastic job! Thank you to Rex Tillerson for his service! Gina Haspel will become the new Director of the CIA, and the first woman so chosen. Congratulations to all!" Trump said on Twitter.
Tillerson joined a long list of senior officials who have either resigned or been fired since Trump took office. Others include strategist Steve Bannon, national security adviser Michael Flynn, Federal Bureau of Investigation Director James Comey, White House Chief of Staff Reince Priebus, health secretary Tom Price, communications directors Hope Hicks and Anthony Scaramucci, economic adviser Gary Cohn and press secretary Sean Spicer.
OUT OF THE LOOP
Trump publicly undercut Tillerson's diplomatic initiatives numerous times.
In December, Tillerson had offered to begin direct talks with North Korea without preconditions, backing away from a U.S. demand that Pyongyang must accept that any negotiations would be about giving up its nuclear arsenal.
The White House distanced itself from those remarks, and a few days later Tillerson himself backed off.
Several months earlier in Beijing, Tillerson said the United States was directly communicating with North Korea but that Pyongyang had shown no interest in dialogue. Trump contradicted Tillerson's efforts a day later.
"I told Rex Tillerson, our wonderful Secretary of State, that he is wasting his time trying to negotiate with Little Rocket Man," Trump wrote on Twitter, using a pejorative nickname for Kim.
Tillerson and Mattis had pressed a skeptical Trump to stick with the nuclear agreement with Iran and other world powers, and Tillerson has taken a more hawkish view than Trump on Russia.
If confirmed by the U.S. Senate after an April committee hearing, Pompeo will be taking over a State Department shaken by the departures of many senior diplomats and embittered by proposed budget cuts.
Lawmakers from both major parties have criticized those cuts and the administration's failure to fill dozens of open jobs there.
But over time, many lawmakers grew to appreciate Tillerson as a relatively steady hand in the chaotic Trump administration.
"He represented a stable view with regard to the implementation of diplomacy in North Korea, Iran and other places in the world," said Senator Ben Cardin, the top Democrat on the Senate Foreign Relations Committee during most of Tillerson's tenure.
(Additional reporting by Steve Holland, Patricia Zengerle, David Brunnstrom, Arshad Mohammed, Susan Heavey, Paul Simao, Lisa Lambert, David Alexander, Makini Brice; Writing by Doina Chiacu; Editing by Bill Trott and Jonathan Oatis)