Partisan differences have stalled a congressional effort to secure sales of ammonium nitrate, after Republicans proposed that potential buyers of the commercial fertilizer have their names checked against the terrorist watch list.

A commonly used fertilizer, ammonium nitrate can also be a key bomb-making ingredient. Ammonium nitrate was used in the 1995 Oklahoma City bombing, the 1993 World Trade Center bombing and the 1998 bombings of U.S. embassies in Africa.

Al Qaeda videos posted on the Internet have shown how to mix ammonium nitrate to make a bomb.

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In an undercover investigation last September, ABC News was able to purchase and store large quantities of ammonium nitrate at stores in Virginia and North Carolina.

The House Homeland Security Committee had convened Tuesday to discuss a bill meant to tighten security around ammonium nitrate sales.  Republican Dan Lundgren, Calif., introduced the amendment that would require potential buyers be screened against the terrorist watch list.

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Democrats immediately objected to the proposal, saying that requiring farmers to undergo the kind of name screening used for airline passengers would place an undue burden on those whose names might match those on the watch list.

"The problem I have is the darn use of the watch list," said Delegate Eleanor Holmes Norton, D-D.C. "Just ask John Lewis and Ted Kennedy about the watch list," she said, naming two senior U.S. lawmakers who have been stopped at airports because their names matched those on the watch list.

While there is an appeals process to clear one's name, Norton said, it can take several months. "The farmer has a limited period of time in which to use that ammonium nitrate. Whereas, I don't know, John Lewis will find his way to Washington one way or the other, even Ted Kennedy."

Rep. Peter King, R-N.Y., the ranking Republican on the panel, professed surprise at the Democrats' position. "How would we explain it if months from now, God forbid, a terrorist pulls off an ammonium nitrate attack, and we didn't even bother to check their name against the terrorist watch list?"

Committee Chairman Bennie Thompson, D-Miss., told ABC News that Democrats supported the idea if innocent farmers whose names falsely match those on the watch list can get their names cleared quickly.  One proposal, backed by the farm lobby, would require the Department of Homeland Security to develop a process to clear false name matches within 72 hours.  Both sides say they expect to reach an agreement soon.