WASHINGTON (Reuters) - President Barack Obama’s first year in office was marked by creeping mistrust between the White House and the Pentagon over Afghan war policy, with repeated requests for more troops fuelling the suspicions, retired General Stanley McChrystal said in a new book.

McChrystal, who became the top US commander in Afghanistan during those months, said Obama was elected at a time when General David McKiernan, then head of international forces, was seeking 30,000 more troops to stave off a Taliban resurgence, a request that had been on hold since the previous summer.

“It created an unwelcome dynamic,” McChrystal wrote in his new memoir, “My Share of the Task.” “In the eighth year of the war in Afghanistan, a new president found himself facing a time-sensitive decision.”

“The next 10 months saw the emergence of an unfortunate deficit of trust between the White House and the Department of Defence, largely arising from the decision-making process on Afghanistan,” he wrote. “To me it appeared unintentional on both sides. But over time, the effects were costly.”

The rising mistrust ultimately played a role in McChrystal’s resignation. In June 2010 the general stepped down after Rolling Stone magazine ran an article entitled “The Runaway General,” in which it quoted members of McChrystal’s staff disparaging top White House officials and allies. McChrystal was summoned back to Washington, where he resigned.

An investigation by the Department of Defence Inspector General concluded that not all of the events described in the Rolling Stone article had occurred as reported and there was insufficient evidence to conclude any Defence Department standards had been violated. Rolling Stone stood by its story.

McChrystal, while expressing surprise about the “tone and direction” of the article, said he accepted responsibility for it and never had any question about the necessary response.

“I knew only one decision was right for the moment and for the mission. I didn’t try to figure out what others might do, no hero’s or mentor’s example came to mind. I called no one for advice,” wrote McChrystal, who now teaches leadership at Yale University and heads a leadership consulting group.

The memoir, which is being released on Monday, offers McChrystal’s first assessment of the events that led to his resignation. It depicts a US military in Afghanistan struggling to find a strategy for success at a time of Taliban resurgence and an inexperienced White House skeptical of the war and sensitive to criticism.

The general portrays himself as well-meaning but slow to understand the administration’s political sensitivities and undercut by his failure to grasp the dynamics of the situation. He wrote that he wanted to operate as independently as possible of political or even policy pressures.

“I found ... the demands of the job made this difficult,” McChrystal said. “The process of formulating, negotiating, articulating and then prosecuting even a largely military campaign involved politics at multiple levels that were impossible to ignore.”

His memoir hits the shelves at a new time of transition in the war whose strategy he helped to devise, with Afghan President Hamid Karzai due to visit Washington this week for talks with Obama.

The two countries are trying to hammer out a deal on the nature of any US troop presence after 2014, when most combat forces are due to leave and hand over security to the Afghan army and police.

The administration is currently studying a residual force of between 3,000 and 9,000 troops to conduct counterterrorism operations and training once most combat troops are withdrawn, a US official said.

That is lower than the preliminary range of 6,000 to 15,000 troops that officials said was initially put forward by Marine Corps General John Allen, the head of international forces. Some defence analysts have warned that those troop numbers are likely to be too small to fulfil the mission.

The current debate over troop numbers echoes the one that McChrystal describes in his book after Obama took office in 2009. The president, who had promised during the election to refocus on Afghanistan and send two additional brigades, found himself facing a request for 30,000 US troops.

The president initially agreed to send 17,000 troops, but the Pentagon soon had to ask for 4,000 more, who were needed for support, making it look as if officials hadn’t done their homework.

Obama ultimately approved the additional troops after announcing a new strategic direction for the war that called for US forces to disrupt, dismantle and defeat al Qaeda and to pursue a counterinsurgency-style strategy in Afghanistan. But the damage had been done.

“The rising mistrust was disappointing,” McChrystal wrote.

After the general was tapped to take over international forces in Afghanistan in May, he conducted a strategic reassessment assisted by civilian defence analysts that concluded at least 40,000 additional troops would be needed to carry out a counterinsurgency strategy.