Washington ? In this era of intense partisanship, it is rare to see congressional Republicans and Democrats join hands, even in a humanitarian cause. Credit Nancy Reagan for helping to spur this political marvel.

The former first lady, as is well-known, lent her prestige last month to the effort to expand the stem cell research that could offer hope of curing diseases such as Alzheimer’s, which afflicts her husband and thousands of others.

It was not a new position for her. But on May 10 she spoke emotionally and powerfully to those — including President Bush — whose actions inhibit such research.

“Ronnie’s long journey has finally taken him to a distant place where I can no longer reach him,” she said. “Because of this, I’m determined to do whatever I can to save other families from this pain. I just don’t see how we can turn our backs on this.”

What has received less attention is that many other Republicans and conservatives, including those who, like Mrs. Reagan, consider themselves staunchly “pro-life,” are stepping forward on this issue.

The result is a bipartisan letter-to-the-president campaign that has taken on surprising dimensions on both sides of Capitol Hill. The letter left the House with 206 signatures — only 12 short of a majority. Among the signers were 36 Republicans, including a dozen ardent conservatives and opponents of abortion.

A companion letter has been circulating in the Senate. Before the Memorial Day break, it had collected 56 signatures, 13 from Republicans. With a majority of the 100 senators already aboard, sponsors are hoping to run the total up to 60 before dispatching it to the White House.

The letter from the House members, circulated by Republican Rep. Mike Castle of Delaware and Democratic Rep. Diana DeGette of Colorado, is eminently respectful of the moral concerns the president cited when he issued the first federal guidelines for stem cell research almost three years ago. In that policy, Bush committed federal funds and resources to expanding the research that might someday prevent Alzheimer’s or Parkinson’s or other crippling diseases — and he has kept his word.

But he said that taxpayer dollars should be used only for work on human embryos destroyed by the date of his speech — not afterward — thereby satisfying those who view the extraction of stem cells from newly fertilized eggs as tantamount to taking of human life.

In their letter, the members of Congress pointed out that the 78 stem cell lines the president thought would be available under his guidelines have shrunk to 15 — not nearly enough to meet the growing research demand. By contrast, there are an estimated 400,000 embryos currently frozen in labs supporting in vitro fertilization clinics — embryos that are in excess of the childless couples’ needs and that likely will be destroyed. The letter writers ask the president to allow couples to donate those eggs for stem cell research.

The signers also note that the research field and the promise of dramatic results have expanded to the point that foreign countries, private institutions and now states are investing heavily in hopes of reaping the rewards from scientific breakthroughs. California voters may have a chance in November to approve a $3 billion bond issue for stem cell research.

But the legislators point out that the National Institutes of Health could set tough ethical standards for all domestic research — if it were able to meet more of the demand for stem cells.

The dialogue between White House and Congress has proceeded in the serious way the subject deserves, with the head of NIH reiterating the president’s stance and the president’s domestic policy chief meeting personally with Castle and DeGette. Nothing has been agreed upon — except the value of continuing to explore the options.

What encourages those who see great hope in this research is the willingness of more and more conservatives to back the president if he adjusts his policy. I spoke with Rep. Randy “Duke” Cunningham of California, a staunch anti-abortion leader, and found him as passionate as Mrs. Reagan about “the miracles” stem cells may provide. Rep. Kay Granger of Fort Worth, a loyal home-state supporter of the president, told me, “I would never ask him to violate his own principles, but we’re not talking about developing embryos for this project; we’re talking about those that would otherwise be destroyed.”

With folks such as these, and with Sen. Orrin Hatch, the Utah Republican leading the effort to collect signatures on the Senate side, the president has plenty of political cover for adjusting his policy. And what a gift to Mrs. Reagan and millions of others that would be!

— David Broder is a columnist for Washington Post Writers Group.