LOUISVILLE, Ky. — U.S. Sen. Rand Paul denounced the use of synthetic drugs but stuck to his position Wednesday that the push to ban the new-wave substances should come from state and local authorities, not the federal government.

The Kentucky Republican is using a procedural maneuver to try to block Senate bills seeking to ban the use of certain chemicals in synthetic drugs such as "bath salts" and other compounds that mimic marijuana, cocaine and methamphetamines.

He said that people who use synthetic drugs are foolish and said he's not opposed to laws against the substances.

"I do think that justice is better served by having the laws locally," Paul told reporters after speaking to a group of conservative lawyers.

One proposal to crack down on synthetic drugs has passed the House, and White House drug czar Gil Kerlikowske has been among the bill's supporters calling on the Senate to follow suit.

Paul did not say Wednesday whether he would try to stymie the House-passed measure, but sounded open to negotiations if supporters are willing to look at some minimum mandatory drug sentences that have been criticized by Paul.

"What we're doing is trying to work with them to say if they will discuss these mandatory minimums," Paul said. "Putting somebody in jail for 20 years for possession of marijuana is too much. I just think that's inappropriate."

Paul's effort to block the legislation would fail if supporters can muster 60 votes to cut off debate. His office has said that the Senate's Democratic leaders can always schedule such a vote.

Kerlikowske said last week that synthetic drugs pose a growing threat to the nation's youth.

His comments came in a conference call that featured a woman from Paul's hometown of Bowling Green, Ky. She spoke of her family's scare last year after her daughter tried synthetic marijuana and wound up in the hospital.

Kentucky Attorney General Jack Conway on Wednesday urged Paul to "stop holding up a vote on this bill." Conway, a Democrat who lost to Paul in Kentucky's 2010 Senate Race, added: "The lives of Kentucky kids are at stake."

"Synthetic drugs are killing or crippling Kentucky kids," Conway said in a statement.

In Kentucky, lawmakers have passed bills to ban synthetic marijuana and bath salts, but authorities say manufacturers have responded by altering the formulas to try to evade the law. State lawmakers are expected to consider a broader measure this year.

At least 39 states have tried crackdowns on synthetic marijuana and bath salts, banning one or both of the drugs, according to the National Conference of State Legislatures.

Kerlikowske last week cited a survey from the National Institute on Drug Abuse that found one in nine 12th-graders reported using synthetic marijuana in the past year. Nationwide, poison control centers have reported sharp increases in the number of calls related to synthetic drugs.

Officials say the powdery substance sold as bath salts mimic the effects of cocaine, ecstasy and LSD. It can be snorted, injected or mixed with drinks or food. The chemicals can cause hallucinations, paranoia, rapid heart rates, violent behavior and suicidal thoughts.

Synthetic marijuana contains organic leaves coated with chemicals that provide a marijuana-like high when smoked.

Authorities say the synthetic drugs can be purchased on the Internet and in some tobacco and smoke shops, drug paraphernalia shops, gas stations and convenience stores.

On another topic, Paul, said Wednesday there's a growing chance that the Republican presidential nominee could ultimately be chosen at a brokered convention this summer. Paul is the son of GOP presidential hopeful Ron Paul.

As the GOP presidential sweepstakes have been scrambled amid the ups and downs of the leading candidates, what once seemed improbable now appears realistic, Rand Paul said.

"I think they're getting bigger all the time," he said of the odds of a brokered convention. "Now it might be 30 percent. I think it really could happen."

The Republican field faces a cross-country series of nine primaries and four caucuses between Feb. 28 and Super Tuesday on March 6. Rand Paul said the chances of a brokered convention will come into clearer focus after that.

The remaining GOP presidential candidates are Mitt Romney, Rick Santorum, Newt Gingrich and Ron Paul.

Rand Paul discounted the chances of a new candidate emerging to win the GOP nomination at the convention.

"I don't see that happening. I think it's going to be one of the four we have."