WASHINGTON -- A key Republican senator has dropped his objection to Gina McCarthy's confirmation to lead the Environmental Protection Agency, potentially clearing her path as Republicans seek to head off Democratic efforts to change Senate rules that allow the minority party to block nominations.

Sen. David Vitter of Louisiana, the top Republican on the Committee on Environment and Public Works, said Tuesday that the EPA had answered sufficient requests he had made in connection with McCarthy's nomination to support moving ahead with her confirmation without a filibuster. McCarthy is one of two Cabinet choices by President Barack Obama who continue to await confirmation. Thomas E. Perez's bid to be labor secretary remains stalled.

"I see no further reason to block Gina McCarthy's nomination, and I'll support moving to an up-or-down vote on her nomination," Vitter said in a statement.

Republicans have also blocked Richard Cordray's nomination as the permanent head of the Consumer Financial Protection Bureau, and blocked progress on confirming new members of the National Labor Relations Board, which would lose the ability to function this year unless it gets new members.

The number of executive appointments on hold in the Senate has caused Majority Leader Harry Reid, D-Nev., to signal that he may try to change Senate rules to weaken the ability of the minority party to block nominations. Under current rules, any nomination can be filibustered, which then requires 60 votes to break. Democrats hold 54 seats, including two independents.

Republicans have argued that there is no need to change the rules. They point to the pace of judicial confirmations to make the case that Democrats have overstated the degree of obstruction they face. On Monday, the Senate confirmed one of Obama's nominations to a federal court of appeals and on Tuesday approved a district court nomination. Approving McCarthy's nomination could give that argument greater strength.

Reid said Tuesday he would convene a meeting of Senate Democrats on Thursday to gauge support for pressing ahead with rule changes. Changing the rules would require 50 votes.

The Senate agreed in January to a more limited rules change to speed up the confirmation of nominees for district courts and sub-Cabinet positions and to enforce existing rules that would make it more difficult to block legislation.

Many Democrats say further changes are necessary, arguing that Republicans have failed to follow through on a commitment to move nominations in a timely manner. The slowdowns this year have included the first-ever filibuster of a defense secretary nominee, Chuck Hagel, who was ultimately confirmed.

But some senior Democrats have opposed the changes that have been advocated by newer Senate Democrats as well as the party's allies in the labor movement. Republican leader Sen. Mitch McConnell of Kentucky has said that employing the "nuclear option" to change filibuster rules could have unintended consequences for Democrats, particularly if Republicans succeed in retaking the majority after the 2014 election.

McCarthy is an assistant administrator at the EPA, and previously worked in the administrations of Republican governors in Connecticut and Massachusetts. She would oversee the effort Obama announced in a recent speech on climate change to develop regulations designed to cut carbon dioxide emissions from existing power plants.

Another Republican, Sen. Roy Blunt of Missouri, said he was continuing to keep a hold on the nomination until progress on a local project was cleared by the administration. But a Republican leadership aide said nothing was precluding Reid from scheduling a vote.