WASHINGTON—The Central Intelligence Agency and its regional partners have drawn up plans to supply more-powerful weapons to moderate rebels in Syria fighting the Russia-backed regime in the event the country’s six-week-old truce collapses, according to U.S. and other officials.

The preparations for a so-called Plan B center on providing vetted rebel units with weapons systems that would help them in directing attacks against Syrian regime aircraft and artillery positions, the officials said.

The Wall Street Journal first reported in February that President Barack Obama’s top military and intelligence advisers were pressing the White House to come up with a Plan B to counter Russia in Syria. Since then, fresh details have emerged on the nature of the new weaponry that could be deployed under the covert program.

The preparations were discussed at a secret meeting of spy chiefs in the Middle East just before the cease-fire took effect on Feb. 27 and in follow-on exchanges between intelligence services.

In those meetings, officials briefed on the deliberations said, coalition members received provisional assurances from the CIA that they would be given approval to expand support to Syria’s moderate opposition. Coalition members have agreed on the outlines of Plan B, but the White House must still approve the list of specific Plan B weapons systems before they can be introduced to the battlefield.