Manchin requested an opinion from Attorney General Darrell McGraw on whether the governor can declare a special election for what remains of the term, and whether it can be set before 2012 when the Byrd would have had to run again.
Manchin said he favors placing the seat on this fall's general election ballot.
"I think 2½ years is entirely too long," Manchin said. "Waiting that long doesn't make any sense to me."
McGraw said Wednesday that his office has begun researching the governor's questions and hoped to respond before Monday.
Byrd was a Democrat, as is Manchin, McGraw and West Virginia's chief elections officer, Secretary of State Natalie Tennant. But the state overwhelmingly went for Republican John McCain in the 2008 presidential race, and a special election would put another Democratic Senate seat in play this year as the party struggles to retain its majority.
Democrats have a 58-41 edge, with Byrd's seat vacant, but are expected to lose seats in November, typical for the president's party in his first midterm elections.
Manchin said he won't arrange to have himself appointed to Byrd's seat. But he had long been expected to run for it in 2012. Asked at a Wednesday press conference if he would be a candidate in a special election, he replied: "I would highly consider that."
Byrd, 92, was the longest-serving senator in history when he died last week with slightly more than 30 months left in his term.
Conflicting state laws and a 1994 state court ruling led Tennant to conclude that whomever Manchin appointed would not have to face voters until 2012. She has since joined the growing chorus seeking to put the seat on this year's ballot.
Rep. Shelley Moore Capito, the GOP's top prospect for the seat, added her voice to that push Wednesday. With Capito already seeking a sixth U.S. House term, campaign spokesman Kent Gates said others have asked her about running for the Senate and she "will look at all options as they come."
Manchin said he will hold off on filling the vacancy until McGraw issues an opinion, but has already compiled a roster of potential choices. He told The Associated Press that it does not include first lady Gayle Manchin, who was rumored to be on the short list.
While not offering specifics, Manchin said the names he's considering have been appeared in media reports. Those earning mentions include former state Democratic Party Chairman Nick Casey; his successor,