Reports of brutality and mistreatment of the American hostages in Iran have been "overblown and exaggerated," Marine Sgt. James Lopez said today.

"Every little piece of information that came out was made to look like more than it was," the 22-year-old ex-hostage told reporters at his first press conference since returning home Wednesday night.

"Some statements I made to my family were misquoted," he said. "It was my fault. The statement I made to my parents that it was so cold that I had to break the ice to get a drink of water, that was a joke. It wasn't quite that cold. The thing about living in a closet for 14 months, my mother understood. I was never actually stuck in a closet. Unless you have very large closets in your house.

"We were treated bad," he said. "But I think our treatment is overblown and exaggerated. I think it's rather imporant that we maintain our integrity. . . . Otherwise we're no better than Iran."

After 14 months in captivity and a week of national homage, Lopez has begun a longer and more difficult journey back to normal life.

Cheered as a hero for holding off the mobs at the American embassy compound in Tehran, singled out by President Reagan for his defiance of his captors, the somewhat overwhelmed youngster is groping for a way back to the Jimmy Lopez who jokingly told a friend on the night of his release to round up all the girls he could find.

Lopez was just a kid when he went to Iran, boasting to his mother just before he left that he would come back famous. "It was the most prophetic thing I ever said," he joked today.

Then, he was the quick-witted, comical Jimmy Lopez who liked to drink beer, chase girls and raise a little hell with his buddies.He was the Jimmy Lopez who once screamed in agony and pounded on a shower wall when he realized that in his excitement at being invited to the apartment of a stunningly attractive woman, he had forgotten to ask her name and apartment number.

Now he is, at his own request, James or Jim Lopez. And he is, not at his request, a model to the nation, the Marine who did what he had to do and who defied his captors with Spanish slogans of American patriotism.

There were flashes of that Lopez today, as he recounted his period of captivity. He criticized American clergymen who painted rosy pictures of life for the hostages, saying he and fellow captives in "Camp Tehran . . . couldn't believe they were buying the garbage the Iranians were putting out."

But he said the worst part of the ordeal was the mental -- not physical -- abuse. "The Iranians didn't know what they were doing," he said. "We were afraid they were going to come in and execute us and then find out they weren't supposed to do it."

He also ridiculed the propaganda displays put on at Christmas by the Iranians as a "giant stroke job," and said that was why he refused to be photographed last Christmas.

"I said to them, 'If you're going to take pictures of me, take them of the situation I'm in and the environment I'm in. You show me after I've been 10 days to two weeks without a shower, you show me when I'm eating a half-baked chicken and raw potatoes. Don't take pictures of me sitting down eating cake and candy."

And when he was asked whether he might participate in a contemplated lawsuit against Iran, he said, "Ma'am, Iran has nothing I want."

But there was a little of the old Lopez, too, who grew his hair long to keep his ears and neck warm and who planned to shave his head this summer if he were still in captivity. He referred to the compound as Hotel California (as in the Eagles' song, "You can check out any time you like, but you can never leave"), and described with natural machismo the "kamikaze" plan of some Marines to stage a raid on the Iranians. "We were going to get this over," he said. "We were going to take down as many as we could, make it expensive for them."

Lopez said he does not know what the future holds, only that he will be a Marine until February 1982 with no plans after then. For now, being a hero is just a little too much. "It's embarrassing," he said.