GENEVA — Iran on Saturday ruled out freezing its uranium enrichment program, casting doubt over the value of its talks with six world powers less then an hour after they started. The talks _ with the U.S. in attendance for the first time _ had raised expectations of possible compromise on a formula under which Iran would agree to stop expanding its enrichment activities. In exchange, the six powers _ including the five permanent U.N. Security Council members _ would hold off on passing new U.N. sanctions against the Islamic Republic. But the comments from Keyvan Imani, a member of the Iranian delegation, appeared to indicate that his government was not prepared to budge on enrichment _ at least going into the talks. “Suspension _ there is no chance for that,” he told reporters gathered in the courtyard of Geneva’s ornate City Hall, the venue of the negotiations. There also appeared to be little progress inside the talks.