The four-year relationship between director Oliver Stone and Arnon Milchan’s New Regency Prods, is on the skids. Sources say the two are deciding whether or not to continue their association, which began in 1991 when New Regency produced Stone’s “JFK” at Warner Bros. The relationship intensified last December when Stone and New Regency set up a production company called Illusion Entertainment.

Although both sides say nothing has been determined, sources say the situation has escalated into shouting matches. Creative Artists Agency, which reps Stone, has stepped in to try to smooth things over.

“Both ‘Evita’ and ‘Noriega’ cost New Regency a lot of money,” said one source with knowledge of the situation.

Both of those Stone projects – “Evita” with New Regency and Cinergi at Hollywood Pictures and “Noriega” with New Regency at Warner Bros. – fell apart over budget and casting last year.

But, the source said, “‘Nixon’ is really at the center of this.”

After Stone requested a bigger budget than the $36 million the production company was willing to put forth, New Regency refused. Stone – with Anthony Hopkins already committed to the project and with New Regency’s consent – approached Fox and Cinergi about “Nixon.”

Fox and Disney – Cinergi’s distributor – reportedly both stepped up with around $40 million for the budget. Discussions have also taken place for “Nixon” scribes Steve Revel and Chris Wilkins to write and Stone to direct a biopic of the slain civil rights leader Martin Luther King Jr., sources say.

Meanwhile, “Nixon” is stuck in a battle of wills. Under terms of the agreement, New Regency has to give Stone permission to let “Nixon” and the filmmaker leave. But Stone and Milchan are contractually obligated to each other for two more Oliver Stone-directed films. “It’s not clear what’s going to happen. It’s a war. A war has broken out and no one knows if (Stone) is going to stay or leave,” a source familiar with the situation said.

“It’s pretty ugly right now,” another insider said.

Stone is holding several projects, including “Alexander the Great.” Meanwhile, “A Bright Shining Lie” – a possible Tom Cruise project with Stone helming – is still at Warner Bros, awaiting the filmmaker.

Another high-profile project, “Wild Horses” is still in the planning stages with Stone at the helm and Joe Eszterhas scripting. That project was to be a co-production between Stone’s Illusion Entertainment and New Regency. But all deals are pending.