WASHINGTON (Reuters) - Veteran U.S. diplomat Anne Patterson is out of the running to under secretary of defense for policy, U.S. officials said on Tuesday, depriving Defense Secretary Jim Mattis of his choice for his top policy adviser. Speaking on condition of anonymity, the officials said  Patterson ran into resistance on Capitol Hill that might have made it hard for her to win confirmation by the U.S. Senate. The Washington Post first reported that Patterson, who had previously served as the top U.S. diplomat for the Middle East and as ambassador to Egypt, Pakistan, Colombia and El Salvador, was no longer a candidate. The newspaper reported that Senator Tom Cotton of Arkansas and Senator Ted Cruz of Texas, both Republicans and members of the Senate Armed Services Committee that would have reviewed her candidacy, opposed her selection. Aides to both did not respond to requests for comment. It was not immediately clear whether Patterson also faced opposition from the White House, though one Trump administration official said there has been a tug-of-war between Mattis and the White House over who should fill the top slots at the Pentagon. “The White House is being met with resistance from Secretary Mattis on almost every single one of our suggestions of who we would like in senior DoD jobs,” said the official, saying “we are basically at a gridlock” but he hoped this would end soon. As under secretary of defense for policy, Patterson would have been the top policy adviser to the defense secretary as well as one of the primary links between the Pentagon and the rest of the U.S. national security apparatus. It was unclear how soon Mattis might offer an alternative for that or other key senior posts that, like many at the State Department, remain empty. 