TRENTON, N.J. — New Jersey’s incoming Democratic governor has promised to legalize marijuana, but just how speedy Phil Murphy and the Democrat-led Legislature can be remains murky.

The effort’s top legislative backers say they have a proposal ready to go soon after Murphy succeeds GOP Gov. Chris Christie on Jan. 16, and Murphy has given no indication of backing off his promise.

But already key Democratic lawmakers are urging caution, and Republicans, trounced in the election, look unlikely to help Murphy deliver on full legalization.

Groups supporting legalization say they expected calls for caution and say it’s better to take a deliberative approach to engender as much buy-in from legislators and the public, as opposed to ramming legislation through quickly.

“I believe we can be thoughtful and methodical in a 100-day window,” said Scott Rudder, president of the New Jersey CannaBusiness Association, a pro-pot legalization trade group.

Justin Singer, an attorney at Feuerstein Kulick, a firm specializing in marijuana law, downplayed legislators’ calls for caution on legalization and says legislators have always understood that to “get it right” they’d need to draw on other states’ successes and failures.

“Transitioning New Jersey from medical to adult use was never going to be as simple as merely getting Murphy elected,” Singer said.

So far, the most prominent legislative proposal comes from Democratic state Sen. Nicholas Scutari. The bill would permit those 21 and older to possess up to 1 ounce of marijuana, 16 ounces of marijuana-infused products in solids, 72 ounces in liquid form and 7 grams of concentrate. It would prohibit home cultivation.

The legislation would establish a Division of Marijuana Enforcement, charged with regulating the industry. The legislation also would establish a sales tax on marijuana from 7 percent to 25 percent over five years to encourage early participation.

Democratic state Sen. Ronald Rice, who represents the state’s biggest city, Newark, is urging caution on proceeding with legalization. He says he wants to hold hearings across the state and is worried about children’s access to edible marijuana and impaired driving.

“We also need to have a better understanding of what the legal sale of marijuana would look like in our state, including where it would be sold and grown,” Rice said.

Murphy has not fully sketched his vision for legalization but has discussed an estimated $300 million in tax revenue that he says would help finance the state’s public pension payments and school aid.

The most prominent GOP opposition has come from Christie, who adamantly opposes legalization; in particular he has criticized the notion of collection tax revenue to help with budget woes while legalizing a drug.

“It’s blood money. It’s disgraceful and it’s disgusting,” he said this week on his regular radio call-in show.

The public seems to be behind the effort. A September Quinnipiac University pollshowed that 59 percent of residents approved of marijuana legalization. The poll surveyed 1,121 voters and has a margin of error of plus or minus 4 points.

Eights states and the District of Columbia have legalized recreational marijuana.