WASHINGTON (Reuters) -Democratic U.S. Senator Kyrsten Sinema on Thursday said she agreed to "move forward" on a $430 billion drug pricing, energy and tax bill, subject to a Senate arbiter's approval of the bill, which Democrats intend to pass over Republican objections.

Senate Majority Leader Chuck Schumer said earlier on Thursday the chamber would convene on Saturday to vote on a motion to proceed and then begin debate on the bill.

The bill known as the Inflation Reduction Act, introduced last week by Schumer and Democratic Senator Joe Manchin, represents a key priority for Democrats and President Joe Biden ahead of November's election battle for control of the U.S. Congress.

With the 100-seat Senate split 50-50, Democrats plan to pass the bill without Republican support through a parliamentary process known as reconciliation.

But they cannot afford to lose support from a single lawmaker. Sinema's agreement was a critical breakthrough. Another worry is COVID-19 -- senators can only vote in person, so Schumer will need his full caucus to be present and healthy to pass the measure if Republicans remain unified in opposition.