MEXICO CITY (Reuters) - A Mexican state could approve medicinal use of marijuana by the end of this year, paving the way for further steps toward legalizing the drug, former Mexican President Vicente Fox said on Monday.

Political pressure inside Mexico to liberalize its stance on marijuana has been rising since the U.S. states of Washington and Colorado legalized possession and sale of the drug for recreational use in 2012.

In July, opposition lawmakers in the western state of Jalisco put forward a plan to change local drug laws, including permitting the use of marijuana for medicinal purposes.

To win support for the plan, the lawmakers from the leftist Party of the Democratic Revolution (PRD) organized an ongoing survey to gauge public opinion, which so far has shown a clear majority in favor of allowing medical marijuana.

Fox, who became a strong advocate for legalization after he left office in 2006, said Jalisco, a traditionally conservative state, was making "rapid progress" with the proposal.

"I think it will probably be approved before the year is over," he told reporters in Mexico City at an event to discuss an energy forum in his home state of Guanajuato next month.

Marijuana, along with contraband such as cocaine and crystal meth, has been a major source of income for violent drug cartels responsible for tens of thousands of deaths in Mexico.

The PRD needs support from President Enrique Pena Nieto's Institutional Revolutionary Party (PRI) to secure a majority in Jalisco's congress, and Enrique Velazquez, one of the lawmakers behind the plan, said nearly half the local PRI deputies had already said they would back legalizing medicinal marijuana.

Much would depend on PRI state governor Aristoteles Sandoval and Velazquez was hopeful he would back the plan, which followed a similar proposal for the capital still under discussion.

"I talked to (Sandoval) 10 days ago, and he was receptive to the idea," Velazquez told Reuters.

In June, Pena Nieto himself hinted that he was open to adopting a more liberal stance on marijuana, saying that Mexico and the United States could not pursue diverging policies on the issue.

In 2009, Mexico made it legal to carry up to 5 grams (0.18 ounce) of marijuana, 500 milligrams (0.018 ounce) of cocaine and tiny amounts of heroin and methamphetamines.

However, advocates of reform say more must be done to cut crime, and Fox said there could be no turning back.

"The path toward legalizing drugs is irreversible," he said. "Prohibition must be replaced by regulation."

(Reporting by Dave Graham and Ana Isabel Martinez; Editing by Lisa Shumaker)