"All administrations face delays in getting some of their nominees confirmed, but the extent of Republican obstruction of Obama nominees is unprecedented," the official said on condition of anonymity.
Obama also rammed through the appointments of US ambassadors to Turkey, Azerbaijan and the Czech Republic, as well as two other administration officials.
The United States withdrew its ambassador to Damascus after Lebanon's former prime minister Rafiq Hariri was killed in February 2005 in a bombing blamed on Syria.
Obama announced his desire to have a new ambassador in Syria in 2009 and named Ford in February this year, part of his policy of reaching out and keeping open communication even with adversaries of the United States.
The administration sees Syria as a crucial link in diplomatic efforts to negotiate peace in the Middle East. It has also hoped to step up intelligence cooperation with Syria, while saying that Ford would directly air US concerns.
Republicans, who swept November mid-term elections, have adamantly opposed the appointment. While not questioning Ford's qualifications, they argue that the United States should not keep an ambassador in a country that supports hardline Islamic movements such as Lebanon's Hezbollah.
Ford, who would likely head soon to Damascus, is a veteran US diplomat in the Arab world. He has served as ambassador to Algeria and held senior posts in the US embassy in Baghdad.
Among the other appointments, Republicans had opposed the nomination of Francis Ricciardone to be ambassador to Turkey, saying he was too soft on promoting democratic rights during a previous stint as ambassador to Egypt.
On the domestic front, Obama appointed James Cole to be deputy attorney general. The Justice Department's number two position has been vacant for nearly half a year as Republicans prevented a vote.
Republicans have grilled Cole over his views on treatment of terrorism suspects as well as his role as an independent consultant to AIG before the insurance company collapsed and received a government bailout.
The Obama administration official justified the recess appointments by saying that the six nominees had waited on average 114 days for a vote in the Senate.
Obama had 79 nominees pending when Congress adjourned last week and has now made 28 recess appointments, according to the official.
At the same time in his tenure, former president George W. Bush had made 23 recess appointments and had six nominees awaiting a vote, the official said.
Under controversial rules, individual senators can hold up nominations at will to show dissatisfaction.