BALTIMORE — When Rafael Palmeiro became the fourth player in major league history to collect 3,000 hits and 500 home runs, his status as a future member of the Hall of Fame seemed somewhat secure.

That topic is again open for discussion, along with a new one: Palmeiro’s credibility.

Five months after telling Congress he never used steroids, Palmeiro on Monday received a 10-day suspension from Major League Baseball after testing positive for a performance-enhancing drug.

The players’ association challenged the positive test in secret proceedings, and the penalty was held in abeyance until arbitrator Shyam Das decided Monday not to overturn it.

No longer able to deny using steroids, Palmeiro insisted he ingested a banned substance by accident.

“When I testified in front of Congress, I know that I was testifying under oath and I told the truth,” the Baltimore Orioles’ first baseman said during a telephone conference call. “Today I am telling the truth again that I did not do this intentionally or knowingly.”

Palmeiro’s peers could only hope he was being honest.

“I don’t know what he’s been taking, but personally I don’t think he’s taken anything illegally,” Chicago White Sox pitcher Mark Buehrle said. “I don’t think he’s ever taken steroids or anything illegally to help himself to play.”

That opinion was shared by White Sox manager Ozzie Guillen.

“It’s a shame,” Guillen said. “If he did it, and a mistake was made, I don’t have anything bad to say about Raffy. Raffy’s a great player.”

Certainly, the numbers Palmeiro has put up are a testament to his greatness. On July 15, he joined Hank Aaron, Willie Mays and Eddie Murray as the only players with 3,000 hits and 500 homers.

Baseball would not say when the positive test occurred, but there’s a chance that he joined that exclusive fraternity while steroids were in his system. If nothing else, those who decide his entrance into the Hall of Fame might wonder if his lofty numbers were the product of talent — or steroids.

“I hope that people look at my whole career and appreciate that I’ve given everything that I’ve got,” Palmeiro said. “I respect the Hall of Fame, and if they think that I’m worthy enough, I would be very honored. And if they don’t, I gave it all that I had to this game.”

Palmeiro, 40, was adamant in his assertion that he accidentally ingested the drug, particularly because on March 17 he declared before a congressional committee, “I have never used steroids. Period.”

Without being specific, the four-time All-Star left the impression that the banned substance was contained in a supplement that was not prescribed.

“Why would I do this in a year when I went in front of Congress and I testified and I told the truth?” he said. “Why would I do this during a season where I was going to get to 3,000 hits? It just makes no sense. ... I’m not a crazy person.”