The state Assembly on Thursday approved a bill that would add California to the growing number of states seeking to legalize the cultivation of industrial hemp — a biological relative of marijuana.

Lawmakers voted 41-30 to pass the bill, sending it to the Senate. If senators also approve it, the proposal would go to Gov. Arnold Schwarzenegger, who has not taken a position on it.

Supporters insist hemp is a safe product that could become a cash crop for farmers because of its use in a long list of products from soap and cosmetics to rope and luggage.

The bill's author, Democratic Assemblyman Mark Leno of San Francisco, said passage of the measure marked a milestone.

"This makes sense," Leno said. "It could provide an opportunity of great value to family farmers. This could be a bonanza of job growth."

But even if the measure becomes law, farmers would still face hurdles to cultivate the plant because hemp contains trace amounts of a banned substance and may still fall under federal anti-drug rules.

Some critics were concerned that allowing hemp to be grown could be the first step to permitting pot.

"You pass industrial hemp today and then something else and then something else," Republican Assemblyman Dennis Mountjoy said. "And then at some point you will get legalized marijuana."

The Drug Enforcement Administration had classified hemp as a controlled substance because an average plant contains small amounts of tetrahydrocannabinols, or THC, the same drug that gives marijuana its intoxicating effect.

Analysts from the Office of National Drug Control Policy said there are also concerns that hemp farms could be used to hide marijuana plants.

But the 9th Circuit Court of Appeals ruled in 2004 that the DEA did not have authority to regulate hemp. Still, Leno said, it remains unclear whether states have the authority to let farmers cultivate the plants.

Processed hemp imported from other countries is sold throughout the United States for manufacturing products. A hemp trade group estimated the annual retail market in the U.S. at $270 million.

A number of states have already passed laws aimed at allowing hemp farming, including Hawaii, Kentucky, Maine, Montana, North Dakota, and West Virginia.

Although the vote Thursday in the Assembly was largely along party lines, Republican Chuck DeVore of Irvine joined Leno as a co-author.

"This measure does not allow the cultivation of marijuana," DeVore said. "All we are doing is legalizing in the United States what is already being done in 30 different nations."