SAN FRANCISCO _ Should a woman be allowed to sell her eggs?

The question had never triggered much debate in the private world of fertility medicine, where Ivy League women can earn tens of thousands of dollars per "donation."

But it seems everything about stem cell research is political.

A spirited disagreement over payment has split feminists, with some calling compensation to research subjects coercive and others contending that banning it is paternalistic.

The dispute has prompted some abortion rights organizations to line up on the issue with conservative Christian groups that oppose embryonic stem cell research.

It also has driven a wedge between two historic allies: stem cell scientists and fertility clinics, which have long relied on an open market for egg sales.

The conflict has been building for years. Human eggs are crucial for stem cell research, but harvesting the eggs entails medical risks, some potentially lethal.

Hoping to preempt a controversy, the authors of California's Proposition 71, approved in 2004, declared that scientists who received grants from the $3-billion state stem cell agency could not pay egg...