President Obama is expected to announce long-anticipated changes in his national security team this week, including a new ambassador to Afghanistan, according to administration officials familiar with internal deliberations. The officials, who provided information on the condition of anonymity, said as many as four high-level appointments could be announced as soon as Thursday, a changing of the guard that would probably involve the naming of a replacement for Defense Secretary Robert M. Gates. A White House spokesman declined to comment on what he said were personnel matters. Senior congressional aides said the administration has not informed national-security-related committees of any firm decisions. But the officials said that Ryan C. Crocker, a five-time ambassador who retired in 2009 after wartime service in Iraq, is likely to be named to take over the U.S. Embassy in Kabul, reuniting him with Gen. David H. Petraeus, who headed U.S. forces in Iraq during Crockers tenure there and now commands the U.S.-led coalition in Afghanistan. Crocker, who has resisted several administration attempts to persuade him to return to service, met privately with Obama early this month, the officials said. A Petraeus-Crocker reunion would be brief, however, with Petraeus due to end his Afghan tour within the next several months. Gatess departure this year has been widely discussed, including by the defense secretary himself. The question facing the White House has been whether to announce a series of related changes all at once or space them out over a period of months. According to Pentagon sources and others, the leading candidate to replace Gates is still CIA Director Leon Panetta. As head of the Office of Management and Budget in the Clinton administration, Panetta helped negotiate the 1993 budget bill, and he is seen as likely to continue the defense procurement and budget reforms Gates has begun. Petraeus, who in Afghanistan has continued the close collaboration with the CIA that he began in Iraq, emerged last month as a contender for the CIA directors job and indicated that he was interested. Marine Lt. Gen. John R. Allen, deputy of the U.S. Central Command, is likely to succeed Petraeus as commander of U.S., NATO and coalition forces in Afghanistan, officials said. This years turnover will also include Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, whose second two-year term ends in September. But officials said that position is unlikely to be included in this weeks announcements. The changes come at a crucial moment for Obamas foreign policy: amid turmoil in North Africa and the Middle East, a U.S. troop withdrawal from Iraq by the end of the year and what the administration has described as a make-or-break summer in Afghanistan. Crocker and Petraeus were widely hailed as a dream team that turned around the Iraq war beginning in 2007, when President George W. Bush ordered a surge in U.S. forces as that country spiraled into sectarian civil strife. Both men have many supporters in Washington. But the Obama administration which kept Gates, a Bush appointee, at the Pentagon even as it criticized Bushs handling of the wars in Iraq and Afghanistan has been reluctant to appear to be further duplicating the Bush team. While long lists have circulated with possible replacements for Gates and Mullen, finding a new ambassador for Afghanistan has been one of the administrations most difficult tasks. Retired Lt. Gen. Karl W. Eikenberry, the current ambassador, is unpopular with the State Department and has frequently been at odds with the government of Afghan President Hamid Karzai. Crockers name has been floated for virtually every senior diplomatic position dealing with the Arab world and South Asia. His likely appointment as ambassador to Afghanistan was reported Tuesday by the Associated Press. Before serving in Iraq, he was U.S. ambassador to Pakistan from 2004 to 2007 and was a senior State Department official on Middle East issues during Bushs first term. In 2002, he was sent to Afghanistan to reopen the American Embassy in Kabul after the Taliban was ousted. Crocker also served as ambassador to Syria from 1998 to 2001, to Kuwait from 1994 to 1997 and to Lebanon from 1990 to 1993. Obama awarded him the Presidential Medal of Freedom, the nations highest civilian award, in 2009 when he retired to become dean of the Bush School of Government and Public Service at Texas A&M;University a position once held by Gates. (WP)