President Bush says he will veto any bill passed by Congress that challenges his policy on embryonic stem cell research. Some lawmakers say stem cells hold great medical promise and Mr. Bush's plan for limited federally funded research must be broadened.

President Bush is holding firm, saying his policy is right for America.

During a conversation with reporters at his Texas ranch, Mr. Bush vowed to veto legislation that goes beyond his proposal. He said he spent a lot of time studying the matter, and will not change his mind.

On Thursday, the President announced plans to go ahead with federally funded research using cells from embryos that had already been destroyed. Some members of Congress say they will fight the restrictions. They say more than 100,000 embryos in the earliest stages of development are in storage in fertility labs and could be used by researchers.

Scientists believe stem cell research could lead to cures for debilitating diseases and injuries. That is because these cells have not yet assumed a specific function in the body and could theoretically be used to repair or regenerate damaged cells or tissue.

But many people say destroying an embryo for research amounts to murder.