By Alice Popovici

ANNAPOLIS, Maryland (Reuters) - The Maryland state Senate voted overwhelmingly on Friday to decriminalize possession of a small amount of marijuana, part of a trend across the United States to ease penalties for pot.

The Democrat-controlled Senate voted 36-8 to make possession of less than 10 grams of marijuana a civil and not criminal offense. It would reduce the penalty to a $100 civil fine instead of a 90-day jail sentence and $500 fine.

The legislation is among bills that lawmakers in Maryland, among the most liberal U.S. states, are considering to ease restrictions on possession of marijuana, including a measure to legalize it.

The bill's sponsor, Baltimore County Democrat Robert Zirkin, during debate cited research showing that reducing the penalty for possession of small amounts of marijuana elsewhere had not resulted in more people using the drug.

"Everywhere, from the 1970s, there's been no discernible effect when you move from criminal to civil," Zirkin said.

Supporters of decriminalization contend it also would help reduce costs of incarceration, adding that blacks have been more likely to be arrested than whites.

Republican Senator Bryan Simonaire, who represents Anne Arundel County and voted against the bill, said the legislation would create inconsistent penalties between alcohol and drug use.

"It sends the wrong message to our children," he said.

The bill moves to the Democrat-controlled House of Delegates, where passage is expected to be more difficult. Zirkin said approval could be eased through amendments approved by the Senate this week.

One amendment requires that, on a third offense, the person found with marijuana appear in court, where a judge could order drug treatment. Another mandates that the civil fine be used in drug treatment programs.

Twenty states, along with the District of Columbia, allow marijuana use as treatment for various health ailments. Washington and Colorado permit cannabis for recreational use.

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While marijuana is illegal under federal law, 15 states and a handful of cities have removed the threat of arrest for possession of small amounts of it.

In the District of Columbia, the city council this month approved a measure decriminalizing marijuana possession.

(Additional reporting by Ian Simpson; Editing by Barbara Goldberg and Gunna Dickson)