"The president is emphatic about this," Rove said, according to a story posted on the newspaper's Web site.
The House has already passed the stem cell legislation, co-sponsored by Rep. Diana DeGette, D-Colo., and Rep. Mike Castle, R-Del.
Rove said he believes the legislation will pass the Senate with more than 60 votes sometime this month "and as a result the president would, as he has previously said emphatically, veto the Castle bill."
Today, DeGette's and Castle's June 7 request to meet with Bush about the issue was denied.
The Bush administration has allowed federal funding only for existing lines of embryonic stem cells, something researchers and patients' groups say hinders vital research.
"We were all an embryo at one point, and we ought to as a society be very careful about being callous about the wanton destruction of embryos, of life," Rove said. He said research shows "we have far more promise from adult stem cells than from embryonic stem cells."
Meanwhile, Rep. Castle argued that the Bush administration may not properly understand what the bill entails.
"This legislation does not expand federal funding for stem cell research; rather it establishes an ethical construct and enables scientists to research the most robust and highest quality lines," Castle explained.
Rove was in Colorado to speak Sunday at an Aspen Institute forum.
Rove also rallied about 400 Republican volunteers at a fundraiser late Monday in suburban Parker, criticizing Democrats for being weak on Iraq and the economy, but he didn't mention the possible veto in his remarks.
He also attended a fundraiser for major donors at the home of Larry Richardson in Denver, party chairman Bob Martinez said.
Rove, who helped the state party raise a total of $200,000, said the major issues in this fall's election would be the economy and Iraq. He criticized Democrats for wanting to pull troops out of Iraq, calling their strategy "cut and run".
He drew applause when he said the world was a better place without Saddam Hussein in power. He said anyone who doubts what the U.S. is fighting for should spend $13.95 to buy a collection of Osama Bin Laden's writings.
"We're in a war with Islamic facists... They want to reestablish and caliphate, an Islamic empire," he said.