WASHINGTON — The Obama administration is considering a plan to use U.S. military trainers to help increase the capabilities of the Syrian rebels, a move that would greatly expand the CIA training now being done in Jordan, U.S. officials said Thursday.

Any training would take place outside Syria, and one possible location would be Jordan.

The officials, who declined to be identified, said discussions were continuing and came as the Obama administration prods Congress to authorize limited military strikes against Syrian President Bashar Assad’s government in retaliation for a deadly Aug. 21 chemical-weapons attack that killed more than 1,400 people.

The proposal to use the U.S. military to train the rebels would answer the demands of some lawmakers, including Sen. John McCain, R-Ariz., to do more to train and equip the Syrian opposition. President Obama in June decided to provide lethal aid to the rebels, but none of that assistance has arrived.

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Officials said Thursday that talk about a military training mission has increased but that there have been no specific Pentagon recommendations forwarded to Obama on how big it should be or how many troops it should involve.

The CIA has been training select groups of rebels in Jordan on the use of communications gear and some weapons provided by Gulf states. The new discussions center on whether the U.S. military should take over the mission so that hundreds or thousands can be trained, rather than just dozens.

Any new training program conducted by the U.S. military
would require getting approvals from the host country, finding appropriate locations, getting the right number of personnel in place to conduct the training and setting up a vetting system to ensure instruction was not provided to rebel groups that may not be friendly to the United States.

The Pentagon has at least 1,000 troops in Jordan, including trainers working with Jordanian forces. The United States left about a dozen fighter jets and a Patriot missile battery there after a recent training exercise.

In St. Petersburg, Russia, meanwhile, Obama pressed fellow world leaders at the Group of 20 economic summit to support a U.S.-led strike on Syria, but he ran into opposition from Russia, China and even the European Union, which condemned the chemical-weapons attack but declared it too soon for military action.

“The use of chemical weapons in Syria is not only a tragedy but also a violation of international law that must be addressed,” Obama insisted during a meeting with Japanese Prime Minister Shinzo Abe on the sidelines of the summit.

China’s G-20 delegation spokesman, Qin Gang, was among those who countered, saying: “War isn’t the fundamental way to solve problems in Syria.”

Obama’s public and private diplomatic wrangling partly was intended to increase pressure on lawmakers in Washington as they debate authorizing military action. The Senate Foreign Relations Committee passed a use-of-force resolution this week, but the measure’s prospects in the full Senate and the House are uncertain.

Although Obama has said he has the authority to order the strike even if Congress says no, aides consider that almost unthinkable.

The prospect of military action against Syria overshadowed the global growth agenda at the two-day G-20 summit, which opened Thursday. Leaders discussed the crisis during a dinner hosted by Russian President Vladimir Putin, an Assad ally.

While Obama has long called for the ouster of Assad, the chemical-weapons attack pushed the United States to the brink of military action for the first time during Syria’s civil war.

The U.S. position on Syria has increased tensions with Putin, who has questioned intelligence reports American officials say link the attack to Assad.

In an interview, Putin said it was “completely ridiculous” to assert that Assad was behind the use of deadly gases against Syrian citizens. The Kremlin also said it was boosting its naval presence in the Mediterranean, where the United States has five destroyers on standby for a military strike.

The European Union (EU) also was skeptical about the effectiveness of military action. EU President Herman Van Rompuy said the chemical-weapons attack “was a blatant violation of international law and a crime against humanity,” but he said a political, not military, solution was needed in Syria.

Chinese officials warned that a strike would raise oil prices and upset the global economy, while Italy’s prime minister said he worried it would widen the conflict.

From the Vatican, Pope Francis wrote a letter urging the leaders “to lay aside the futile pursuit of a military solution.”

The G-20 meeting put on full display the increasingly awkward and tense relationship between Obama and Putin. To protest Russia’s decision to grant temporary asylum to Edward Snowden, the former National Security Agency contractor who disclosed secret programs, Obama last month canceled a separate one-on-one meeting in Moscow and declined even a private session in St. Petersburg.

As he arrived at Constantine Palace, Obama was greeted by Putin, and the two shook hands and smiled in a businesslike encounter lasting about 15 seconds.

In the run-up to his encounter with Obama, Putin sent mixed signals on Syria. He has said he would be open to a military strike if the United States could tie the Aug. 21 poison-gas attack in Damascus’ suburbs to Assad’s military. But he also made it clear he had no confidence in U.S. intelligence reports.

Hours before Obama’s arrival, Putin accused U.S. Secretary of State John Kerry of lying to Congress about the situation in Syria.

Ben Rhodes, deputy national-security adviser, said the United States would share its evidence with Russia, but called Putin’s speculation that opposition forces could have launched the attack “implausible theories.”

On whether the top U.S. diplomat was a liar, Rhodes said: “We certainly would side with Secretary Kerry in that back-and-forth.”

Material from The New York Times and the Tribune Washington Bureau is included in this report.