His actions are based on strong religious beliefs on the part of some conservative Christians, and presumably the president himself. Such convictions deserve respect, but it is wrong to impose them on a pluralistic nation.

Bush threatened this week to veto a modest research-expansion bill that was approved by the House and is likely to be passed by the Senate.

The reason, he said, is that the measure would "take us across a critical ethical line" by encouraging the destruction of embryos from which the stem cells are extracted.

Never mind that this particular ethical line looms large only for a narrow segment of the population. It is not deemed all that critical by most Americans or by most religious perspectives.

Rather, the president's intransigence provided powerful proof of the dangers of letting one group's religious views dictate national policy.

Clumps of Cells

The president's policy is based on the belief that all embryos, even the days-old, microscopic form used to derive stem cells in a laboratory dish, should be treated as emerging human life and protected from harm.

This seems an extreme way to view tiny laboratory entities that are no larger than the period at the end of this sentence and are routinely flushed from the body by Mother Nature when created naturally.

These blastocysts, as they are called, bear none of the attributes we associate with humanity and, sitting outside the womb, have no chance of developing into babies.

Some people consider them clumps of cells no different than other biological research materials. Others would grant them special respect but still make them available for worthy research.

But Bush is imposing his different moral code on both, thereby slowing research that most consider potentially beneficial.

The president drew his line in the sand back in 2001 when he decreed that federal funds could be used only for research on stem-cell lines that already existed.

His rationale was that the embryos that yielded those lines had already been destroyed but he did not want to encourage any more destruction, even if the embryos came from fertility clinics' surplus stocks that were ultimately to be discarded.

'No Such Thing as a Spare Embryo'

Unfortunately, only about 20 lines have become available under his policy, and most suffer from problems that make them unsuitable for certain kinds of research.

Scientists want access to more surplus embryos and the ability to create embryos in the laboratory, ideally with federal financing.

The bill just passed by the House would ease the problem by allowing federal money to support research on a much wider array of stem cells derived from embryos that would otherwise be discarded.

Although that seems an extremely modest step, Bush countered with a stagy show in which he was surrounded by babies and toddlers born of test-tube embryos that were implanted in women eager to have children.

"There is no such thing as a spare embryo," he said, noting that a Christian program for embryo adoption has already led to 81 births, with more on the way.

The implication was that surplus embryos should be used to produce children, not stem cells, but it seems unlikely that such programs, which have to rely on people who are willing to allow others to give birth to and raise their genetic offspring, can make much of a dent in the stock of 400,000 surplus embryos at fertility clinics.

There will be thousands of embryos available for research should Congress find the will to pay for it.

Imposing His Morality

Unfortunately, none of this week's heated debate focused on the most promising area of stem-cell research: research cloning or therapeutic cloning.

Bush is adamantly opposed to such research, which involves creating microscopic embryos to derive stem cells that genetically match a diseased patient, thus facilitating research on particular diseases and ultimately potential cures.

There, too, he seeks to impose his morality on a society with pluralistic views.