WASHINGTON — It's easy for Congress to meddle with the District of Columbia's decision to legalize recreational use of marijuana, but taking on the states is a different matter.

A catch-all spending bill Congress passed last week would prevent the District from using federal and local money to implement any law or regulation that repeals or reduces marijuana-related penalties. The action is in direct response to a voter initiative passed last month that allows possession of up to 2 ounces of pot or up to three mature plants for personal use.

The Constitution gives Congress the power to review and possibly reject all legislation approved by the District's elected officials or its citizens.

Congress has less leverage with the states, and thwarting efforts supported by a plurality of voters back home could prove risky at election time.

"That's sort of asking for a head-on collision with states' rights," said Philip Wallach of the Brookings Institution, a Washington-based think tank.

Wallach said the most ready tool at Congress' disposal in persuading states to keep marijuana illegal would be to withhold money for certain programs if state marijuana initiatives conflict with federal law. That's something Rep. Trent Franks, R-Ariz., chairman of a House panel on the Constitution and civil justice, says he's prepared to support.

Franks said the marijuana legalization movement endangers youth. Many other Republican lawmakers don't seem ready to take such concrete steps, including Sens. Charles Grassley of Iowa and Ron Johnson of Wisconsin, the likely chairmen of committees that could deal with marijuana laws in the next Congress.

Grassley wasn't prepared to say what issues the Judiciary Committee will focus on; Johnson said he'd like a hearing by the Homeland Security and Governmental Affairs Committee on how marijuana legalization is working but that's as far as he would commit.

The Justice Department has said it will not stand in the way of states that want to legalize, tax and regulate marijuana as long as there are effective controls to keep it away from kids, the black market and federal property.

Proponents of marijuana legalization know exactly where they want to go next. Their itinerary includes pushes into California, Arizona, Nevada, Maine and Massachusetts. There's money to be raised for campaign ads, ballot initiatives to write and petition campaigns to organize. Four states have voted to legalize marijuana: Washington and Colorado first, followed by Oregon and Alaska.

"Republican Senate or not, we're going to keep moving forward," said Bill Piper of the Drug Policy Alliance, which advocates an overhaul of drug policy.

The group points to another section of the just-passed spending bill as evidence that most lawmakers don't want Congress to interfere with state decisions regarding marijuana. That provision would prevent the Justice Department from using money to prosecute medical marijuana patients or distributors who are in compliance with their state's laws.

Twenty-three states have legalized medical marijuana, according to the National Conference of State Legislatures.

The GOP's most consistent backer of the legalization movement, Rep. Dana Rohrabacher of California, said he's simply unsure where a Republican-controlled Congress will take the marijuana issue.

"I can't read my fellow Republicans on this," he said. "Behind the scenes, they will tell you, 'Oh, yeah, (prohibition) is stupid, but I'm not going to risk my political career.'"

Republican Rep. Andy Harris of Maryland, an anesthesiologist who has led the congressional effort to halt the District of Columbia's marijuana initiative through September 2015, said prohibiting recreational marijuana use is the right thing to do, whatever the politics.

"If we can educate the public about the hazards, especially given the high unemployment rate among D.C. youth, the problems they have in the educational systems, I think we can convince people the last thing they need in the District of Columbia is legalization," he said.

The effort to legalize marijuana in the District was spurred by concerns about racial disparities in marijuana arrests, with black people making up about 90 percent of marijuana arrests, yet only about half of the city's residents.

Asked whether Republican leaders were ready to take on the legalization trend elsewhere, Harris said he would agree the issue is not a priority for them.

"The plate of leadership is so full with foreign affairs and economic matters in this country, this is just not on their radar screen," he said.

Said Wallach from Brookings: "It probably makes political sense for a lot of people to just lay low on this issue."