WASHINGTON (AP) — On the eve of new talks, President Barack Obama is plunging ahead in search of a nuclear agreement with Iran despite outright opposition from American allies in the Middle East and deep skepticism, if not open hostility, from Congress.Iran is pressing ahead in its own way, trying to make a deal more likely to ease painful economic sanctions without losing its own hardliners at home.There was a fresh sign of efforts to make headway as negotiators from Iran, the five permanent members of the U.N. Security Council and Germany prepared for Wednesday’s new round of talks in Geneva. British Prime Minister David Cameron contacted Iranian President Hassan Rouhani in the first such conversation between the leaders of the two countries in more than a decade.Cameron’s office said the leaders agreed during their telephone conversation that significant progress had been made in recent talks and that it was important to “seize the opportunity” in this week’s new negotiations.Obama’s willingness to embrace a pact that falls short of Security Council demands for Iran to halt uranium enrichment has pushed his administration’s already contentious relationship with Israel to the brink, strained ties with Gulf Arab states and exacerbated tensions with Democratic and Republican lawmakers.Although everyone claims to have to same goal — preventing Iran from developing atomic weapons — the rancorous, public disagreement over how to achieve it has driven a wedge between the administration and those who the administration insists will benefit most from a deal.Opponents say Iran is getting too much in the way of sanctions relief for too little in the way of concessions. And, they argue, Iran just can’t be trusted. Obama and his national security team counter that the risk is worth taking. The alternative, they say, is a path to war that no one wants.In the run-up to the new talks, Iranian President Hassan Rouhani conceded a longstanding demand that Iran’s right to enrich uranium must be recognized in any deal, and that incited opposition from hardliners in the his country. Also, speaking to reporters in Rome while en route to the negotiations, Iranian Foreign Minister Mohammed Javad Zarif accused Israel of trying to “torpedo” a possible agreement. Obama, along with Secretary of State John Kerry and National Security Adviser Susan Rice, personally appealed to senators in a White House meeting to hold off on seeking additional sanctions in order to test Iran’s seriousness in addressing concerns it is trying to develop nuclear weapons.“We have the opportunity to halt the progress of the Iranian program and roll it back in key respects, while testing whether a comprehensive resolution can be achieved,” the White House said in a statement after the two-hour meeting Tuesday. It said if there is not an initial agreement, Iran will keep making progress on increasing enrichment capacity, growing its stockpiles of enriched uranium, installing new centrifuges and developing a plutonium reactor in the city of Arak.