WASHINGTON (Reuters) -U.S. Democratic Senator Joe Manchin, a pivotal vote in the evenly divided Senate, said on Wednesday he was opposed to a process called reconciliation that makes it easier to pass bills without Republican support, a potential blow to President Joe Biden's chances of passing a huge infrastructure measure.

Manchin also said he would not support any step to weaken the ability of Republicans to mount filibusters to block legislation. Some Democrats want to toss aside the filibuster rule, which requires 60 votes in the 100-member chamber to approve most bills.

"I simply do not believe budget reconciliation should replace regular order in the Senate," Manchin said in an opinion piece in the Washington Post. "Senate Democrats must avoid the temptation to abandon our Republican colleagues on important national issues."

Democrats relied on the budget reconciliation process to avoid a possible Republican filibuster and pass Biden's $1.9 trillion coronavirus relief bill in March with a simple majority in the Senate. They have been considering doing the same with Biden's proposed infrastructure package.

"The filibuster is a critical tool to protecting that input and our democratic form of government. That is why I have said it before and will say it again to remove any shred of doubt: There is no circumstance in which I will vote to eliminate or weaken the filibuster,” Manchin said.

"Every time the Senate voted to weaken the filibuster in the past decade, the political dysfunction and gridlock have grown more severe," Manchin wrote, saying it was time to end "political games" and return to a "new era of bipartisanship."

The centrist Democrat from West Virginia said last month he could see making filibusters more "painful" to carry out, although he was not in favor of eliminating them.

Biden said two weeks ago that the procedural maneuver was being misused "in a gigantic way" and should be more difficult to carry out. He said he favored a return to the "talking filibuster" - a tradition from decades ago that required senators to occupy the floor and make their case against legislation if they opposed it.

Manchin has been willing on some issues to cross party lines, so his support is crucial to any bill passing in the 50-50 Senate. Democrats control the chamber because Vice President Kamala Harris can break a tie.

The Senate parliamentarian ruled on Monday that Democrats could use reconciliation to pass more legislation this year, and Democrats were considering using the process to pass Biden's infrastructure investment package.

Biden wants to spend $2.3 trillion on roads and bridges, retrofitting homes, expanding broadband internet access, caring for the elderly, building up domestic manufacturers and building high-speed rail, a proposal that has run into stiff opposition from Republicans.

(Reporting by Eric Beech; Editing by Mohammad Zargham and Grant McCool)