The story told yesterday by Secretary of State George P. Shultz about the high-level struggle to influence President Reagan and his Iran policy contains "elements of an internal coup," Sen. Sam Nunn (D-Ga.) said yesterday in one of many outspoken reactions from members of the Iran-contra committees.

"People . . . were giving the president of the United States bad information and preventing him from making decisions on accurate facts," Nunn said, apparently referring to former national security adviser John M. Poindexter and the late William J. Casey, former director of the CIA.

"He told a story that indicated the president of the United States has been abused," Nunn said. "He's been manipulated. He's been intentionally misled. In some cases, he had been left out of important decisions.

"I think it's been an astounding day," he said.

Sen. William S. Cohen (R-Maine) called Shultz's testimony "the most extraordinary, certainly, that I've heard in my 15 years in Congress."

Cohen said Shultz had taken his audience "back stage, as it were, behind the White House doors." He added: "I think we all knew that there is always a power struggle that takes place within any administration, . . . but I think the degree of pettiness that was revealed in the power struggle was surprising to most."

"It has a profound impact," Cohen said. "It is really having a power on the membership. Americans tend to be hooked on fast food and junk films. You're looking at a man who is offering you a full-course meal on constitutional government."

Sen. David L. Boren (D-Okla.) said Casey and Poindexter clearly tried "to cut him {Shultz} out.

"I think they knew he was giving strong advice to the president at every opportunity," Boren said. "I think they were afraid if he saw the president too often, that he might change the president's mind. I think they were deliberately shielding the president from this kind of advice Secretary Shultz was giving him."

Rep. Dante B. Fascell (D-Fla.) said he always felt Casey was the pivotal figure: "Mr. Casey was not only director of the CIA, but director in general of policy."

Sen. Paul S. Sarbanes (D-Md.) said: "I find it incredible that the secretary of state was dealt out of even knowing that the president had signed these findings with respect to the transfer of arms to Iran."

Sen. George J. Mitchell (D-Maine) said: "It was a truly incredible degree of internal deception within the administration."

Sen. Paul S. Trible (R-Va.) said Shultz's testimony was "devastating in its portrayal" of Poindexter's role. "Neither the president nor the secretary of state were being told the truth about the {National Security Council} activities," Trible said. "Indeed, in George Shultz's word, they were being deceived and lied to. It's a very sad story."