Palmeiro became the highest-profile player among the seven who have failed a test under the toughened major league policy that took effect in March, rules criticized by Congress as not being stringent enough.
In a conference call Monday, Palmeiro said he never intentionally took steroids and could not explain how the drugs got into his body. CBS News Correspondent Howard Arenstein reports that he offered little explanation beyond saying he made a mistake.
He also apologized and said would accept his punishment.
"I have never intentionally used steroids. Never. Ever. Period," he said. "Ultimately, although I never intentionally put a banned substance into my body, the independent arbitrator ruled that I had to be suspended under the terms of the program."
The 40-year-old is the seventh player to test positive for steroids under the policy adopted earlier this year. Palmeiro doubled on July 15 to join Hank Aaron, Willie Mays and Eddie Murray as the only players with 3,000 hits and 500 homers.
Palmeiro said the arbitrator "did not find that I used a banned substance intentionally — in fact, he said he found my testimony to be compelling," but still ruled that he needed to serve the suspension. Palmeiro wouldn't go into the specifics but left the impression that the banned substance was contained in a supplement that was not prescribed.
A grievance filed by the players' union against the suspension was denied by arbitrator Shyam Das.
Appearing with Mark McGwire, Sammy Sosa and other baseball stars before a congressional committee on March 17, Palmeiro made an opening statement in which he said: "Let me start by telling you this: I have never used steroids. Period. I don't know how to say it any more clearly than that. Never."
Palmeiro was so emphatic in his denial of steroid use that he pointed his index finger at the panel, and expressed indignation over accusations made by former slugger Jose Canseco, who cited Palmeiro as a steroid user in his tell-all book. In an interview on the
Government Reform Committee chairman Tom Davis, R-Va., who led the steroids inquiry, was traveling out of the country on Monday and couldn't be reached for comment, spokesman Rob White said.
"If true, this is disheartening news for those of us who believed Mr. Palmeiro was a key ally in our effort to rid sports of performance enhancing drugs," White said.
White House spokesman Scott McClellan said President Bush considers Palmeiro "a friend and he believes him" when he says he never intentionally took steroids.
On July 7, Palmeiro took part via conference call in a round-table discussion about how to rid sports of steroids with Davis and representatives from the NFL, NBA, NHL and Major League Baseball.
Palmeiro seemed contrite on the conference call, saying he hoped there was something to be gained from his suspension by educating players to be more careful about what they put in their bodies.
"I want to apologize to MLB, the Baltimore Orioles organization, my teammates, and most of all, my fans," Palmeiro said. "Given my role with the No Tolerance Committee and my relationships with Congress, I feel the need to communicate a serious message to my fellow players and to kids everywhere."
Palmeiro played against the White Sox on Sunday night, but began serving his suspension immediately and was not in the lineup for the start of Monday's home game against Chicago. He stands to lose $163,934.42 of his $3 million salary during the suspension.
Orioles owner Peter Angelos expressed support for Palmeiro in Monday's conference call.
"I am truly saddened by today's events," Angelos said. "I have known Rafael Palmeiro for many years. ... I know from personal experience that his accomplishments are due to hard work and his dedication to the game."