WASHINGTON (Reuters) - The United States is ready to step up covert aid to Syrian rebels under a plan being discussed with regional allies including Saudi Arabia, according to a Washington Post report.

The plan includes CIA training of about 600 Syrian opposition forces per month in Saudi Arabia, Jordan and Qatar, foreign affairs columnist David Ignatius wrote on Thursday. That would double the forces currently being trained in the region.

The Obama administration was debating whether to use U.S. Special Operation forces and other military personnel in the training, something Syrian rebels have argued would carry less political baggage than the CIA, according to the column.

President Barack Obama was en route Friday to Saudi Arabia, which has been a strong supporter of Syria's rebels but has clashed with Washington over how aggressively to intervene in Syria.

Deputy national security adviser Ben Rhodes told reporters on Air Force One there was no announcement planned on additional aid. He said Saudi-U.S. cooperation in helping the Syrian opposition had improved over the last several months and would be a topic of conversation during Obama's Riyadh visit.

The Obama administration has been criticized by some in Congress for failing to do more in Syria, where 140,000 people have been killed, millions have become refugees and thousands of foreign militant fighters have been trained since 2011 as rebels fought to oust President Bashar al-Assad.

Washington was also considering whether to provide the rebels with anti-aircraft missile launchers, known as MANPADS, to stop Assad's air force, the column said. Saudi Arabia wanted U.S. permission before delivering them, it said.

The plan, which was still being formalized, also called for vetting of opposition forces for extremist links during and after training, according to Ignatius.

Qatar has offered to pay for the first year of the program, which could cost hundreds of millions of dollars, according to the column. The program would try to stabilize Syria by helping local councils and police in areas not under Assad's control and seek to establish safe corridors for humanitarian aid, it said.

(Reporting by Doina Chiacu; Editing by Marguerita Choy)