Some Massachusetts towns have given up enforcing a law that decriminalized the possession of small amounts of marijuana, saying the law is written with too many loopholes to be effective.

The law established a civil fine of $100 for those caught with an ounce or less of marijuana. That replaced what had been a criminal offense carrying a maximum penalty of six months in jail and a $500 fine, also for possession of an ounce or less of the drug.

But the law — overwhelmingly passed as a ballot measure in November 2008 — does not require offenders correctly identify themselves nor does it provide a way to force them to pay the fines.

That has led to a patchwork of enforcement across the state, with some communities handing out hundreds of civil citations and others turning a blind eye to personal marijuana use.

"A number of communities have tried, but a number have just given up," said Wayne Sampson, executive director of the Massachusetts Chiefs of Police Association.

Police officials say that with most civil citations, such as speeding tickets, there are repercussions for those who don't pay the fines. In some cases, police can even levy criminal charges against people who fail to pay.

But they cannot do so in the case of possession of less than an ounce of pot. The only recourse for city and town clerks offices is to take offenders to small claims court, which clerks say isn't worth the time or effort to recoup $100.

"The ticketing of the individuals isn't effective without a back up or other consequences for nonpayment of fines," New Bedford Police Chief Ronald Teachman said.

Other officers say they're handcuffed because the law doesn't require people caught with small amounts of marijuana to provide identification.

"If they tell you their name is Yogi Berra or Ronald McDonald, nothing allows for further positive identification," Sampson said.

Police chiefs have pushed for legislation to strengthen the law's enforcement and to require offenders identify themselves, but Sampson said legislators suggested they wait until the law had been in effect longer.

Despite the challenges, officials in the state's major cities said they are still enforcing the law by handing out civil citations to violators.

"Our job is to enforce the laws," Worcester police spokesman Sgt. Kerry Hazelhurst said. "That is what we have been doing."

Springfield has handed out 730 citations since the law took effect in January 2009, said Sgt. John Delaney of the Springfield Police Department.

"The people that are using marijuana are still very conscious of the fact that marijuana is not legal," Delaney said.

Some cites and towns also have passed bylaws prohibiting marijuana use in public and increasing the fines for marijuana possession.

Supporters of the ballot measure said law enforcement officers have all the tools they need to enforce the law effectively. They say the law has not ushered in an era in which consumers can smoke with impunity.

"Decriminalization is never society sanctioning the use of marijuana, it is reducing the cost of interactions with police," said Allen St. Pierre, executive director of the National Organization for Reform of Marijuana Laws.