WASHINGTON - Nancy Reagan is poised for a quiet entrance into the Senate's embryonic stem cell debate in much the same role she played during the fierce fight in the House, calling up wavering lawmakers to help win passage of legislation in the shadow of President Bush's veto threat.

"This is a very important issue to her and I know she remains committed to the cause and will do what she can at the right time," her spokeswoman, Joanne Drake, said in an interview Thursday.

Douglas Wick, the Hollywood producer who said he persuaded President Reagan's widow to speak out on the issue, agreed.

"Certainly when the Senate fight becomes clear, she will be involved again," said Wick, whose father, Charles, was director of the U.S. Information Agency during the Reagan administration.

"She prefers to work behind the scenes, as she did in the House," Wick said.

They spoke on the day Mrs. Reagan had taken a fall in her London hotel room. She was taken to a hospital for examination and released, Drake said.

Acknowledged by those on both sides of the stem cell issue to be the most powerful advocate involved, the former first lady wields her influence quietly - a rarity in a loud debate pitting advocates who believe stem cell research could lead to cures for diseases such as Alzheimer's against opponents, like Bush, who say it is wrong to destroy human embryos to possibly save lives.

Congress is working on legislation that would lift Bush's 2001 restrictions on federal funding for new stem cell lines developed from days-old embryos. The bill passed the GOP-controlled House by a comfortable margin, but it did not attract enough votes to overcome a presidential veto.

Now Mrs. Reagan and other advocates have turned their sights on the Senate, where a bipartisan group of sponsors say they have at lest 58 votes in favor of the House-passed bill - two short of the number required to stop a promised filibuster. Senate Majority Leader Bill Frist, R-Tenn., a physician and White House ally, said he expects the chamber to act on the bill next month.

For Mrs. Reagan, the stem cell issue is personal: Six years after his second term ended, President Reagan announced in 1994 that he had been diagnosed with Alzheimer's disease. Millions watched a decade later when Mrs. Reagan escorted his body on a cross-country memorial tour and finally collapsed, weeping, over the coffin.

Central to Mrs. Reagan's message is the notion that supporting the bill is consistent with anti-abortion policy, say those who have spoken with her.

"She makes a very good case for why this is something that somebody who cares very much about respect for life also cares very much for the respect for the living," said Rep. Darrell Issa, R-Calif.