WASHINGTON, Sept. 3, 2013  -- Former Secretary of State Hillary Clinton today endorsed President Obama's plan for limited U.S. military action in Syria, giving a boost to the administration as it mounts a full-court press to win over Congress and the public.

"Secretary Clinton supports the president's effort to enlist the Congress in pursuing a strong and targeted response to the Assad regime's horrific use of chemical weapons," a Clinton aide told ABC News.

The comments come at a key moment, before an expected congressional vote next week on a resolution that would authorize Obama to use force in Syria against the Bashar al-Assad regime.

Clinton, who supported a more aggressive U.S. approach to Syria during her tenure as secretary, adds influence to the administration's so-called "flood the zone" strategy to lobby members of Congress.

Her high profile and popularity could prove particularly helpful in convincing skeptical progressive and Democratic allies.

Since she left office in February, Clinton had been conspicuously absent from the Syria debate. Her parting comments, in an exit interview with ABC News, defended the administration's Syria strategy as "productive" in addressing an "extremely complex problem."

After allegations of a horrific Syrian chemical weapons attack surfaced last month and the Obama administration prepared a response, Clinton remained silent, even as other recent Obama administration alumni, including former Defense Secretary Leon Panetta, and several of the president's political rivals, spoke out.

Panetta, who also left the administration in February, made a forceful public case Friday, arguing that Obama has "responsibility" to take action against Assad for the alleged use of chemical weapons.

"When that line has been drawn and action needs to be taken, then the U.S. ultimately has to do that for the sake of the world and for the sake of world peace," Panetta told NBC News.

Clinton's critics had suggested she might have been trying to avoid taking a position on military intervention because of concerns about how it might affect her possible presidential run in 2016. Her 2002 vote authorizing President George W. Bush's invasion of Iraq became a point of contention during the 2008 primary debate.

Clinton may address the Syria situation at greater length one week from today when she steps back into the national spotlight for a high-profile speech at the Constitution Center in Philadelphia.

The speech, she said publicly last month, will "talk about the balance and transparency necessary in our national security policies, as we move beyond a decade of wars to face new threats." It will come just as the debate in Congress over a use-of-force authorization measure is coming to a head.

Clinton also said recently that she would "address the implications of these issues for America's global leadership and our moral standing around the world."

While Secretary of State John Kerry, Defense Secretary Chuck Hagel, National Security Adviser Susan Rice and other top officials lead the messaging blitz on Syria, the White House is also enlisting the support of other high-profile former members of Obama's inner circle.

Former senior strategist David Plouffe, press secretary Robert Gibbs, National Security Council spokesman Tommy Vietor and speechwriter Jon Favreau all converged on the White House on today to assist with the sales pitch on military action.

The president has also gotten a rare and significant boost from former presidential rival Sen. John McCain, House Speaker John Boehner, and several past secretaries of state, including Condoleeza Rice and Madeleine Albright.