-- Baltimore Orioles first baseman Rafael Palmeiro, who had defiantly denied using steroids during a congressional hearing on performance-enhancing drugs in March, was suspended Monday for 10 days for violating baseball's anti-drug policy.

Although Major League Baseball officials declined to identify the substance Palmeiro was found to have used, a well-placed industry source said it was "a serious steroid."

Palmeiro, who on July 15 became one of only four players in major league history with 3,000 hits and more than 500 home runs, said he tested positive for a steroid but does not know how it got into his system. He appealed the suspension but an arbitrator ruled against him.

"Why would I do that in a year when I went in front of Congress and I testified and I told the truth?" Palmeiro said. "Why would I do this in a season when I was going to get to 3,000 hits? It makes no sense. I would not put my career on the line. I would not put my reputation on the line and everything that I've accomplished throughout my career. . . . I'm not a crazy person. I'm not stupid. This is something that's an unfortunate thing. It was an accident. I'm paying the price."

President Bush, the owner of the Texas Rangers when Palmeiro played for that team, told reporters Monday that he believes him.

"Rafael Palmeiro is a friend. He testified in public and I believe him," Bush said in an interview with the Knight Ridder news service. "He's the kind of person that's going to stand up in front of the klieg lights and say he didn't use steroids, and I believe him. Still do."

On March 17, Palmeiro, Orioles teammate Sammy Sosa and retired sluggers Jose Canseco and Mark McGwire testified before the House Government Reform Committee investigating steroid use in professional sports. Emphatically pointing a finger toward legislators as he spoke, Palmeiro testified that "I have never used steroids. Period."

The panel found Palmeiro's testimony so compelling that he was asked to join a task force on steroids. Palmeiro had participated in several task force discussions and took part in a conference call last month with several representatives from other pro leagues.

"I'm disappointed, surprised certainly," Rep. Stephen Lynch (D-Mass.), a committee member, said by telephone. "At the hearing, out of all the players, I got the sense that Mr. Palmeiro's testimony was the most passionate and convincing. This latest evidence certainly doesn't help Mr. Palmeiro's case. We've given baseball and the union a chance to straighten itself out. . . . Maybe it's time for Congress to step in."

Rep. Elijah Cummings (D-Md.), another committee member, said he would "look into the possibility" that Palmeiro committed perjury by testifying that he didn't use steroids.

"The way he comes off is, 'Look, they were in my body, but it must have been an accident.' That's like talking out of both sides of your mouth," Cummings said. "I just wish he had been more forthcoming. I think people can accept that he made a mistake, but when you say, 'Yeah, I accept the punishment, but I really didn't do it,' then it gets kind of murky."

Steroid testing is done with a process called gas chromatography/mass spectrometry, which can detect in urine the chemical signatures of the components of steroids. If the test detected the breakdown products of the steroid called stanozolol, there is virtually no doubt that Palmeiro used a banned substance, said Gary Wadler, a steroid expert at New York University.

"It has a unique fingerprint. It can't be mixed up with anything else," Wadler said.

But if the test detected a substance known as nadolone, which is one of the most commonly found in steroid tests, it would be evidence that Palmeiro had taken the steroid known as Andro. And that steroid is known to have contaminated permissible protein powders sold in many nutritional supplement stores.

"The manufacturers of dietary supplements have problems with contamination of their products, such as their protein powders. Someone might take a protein powder and the next thing they know they show up positive," Wadler said. "It's a very possible scenario."

An Orioles team official who requested anonymity said Baltimore players were repeatedly warned about using substances that could violate baseball's drug testing policy.

"Whether or not it was accidental, you're kind of disappointed in the guy, too. It's depressing," said the team official. "The doctors and the trainers have been harping on this stuff all year. There was no one in that clubhouse who was uneducated about what you should or shouldn't be putting into your body."

Palmeiro declined to talk about the specifics of his testing or the subsequent appeal filed by the players' union because the proceedings are confidential under baseball's labor agreement. It is not known if the test was taken before or after Palmeiro testified.

Palmeiro is the seventh player caught since baseball, after tense negotiations with the union, implemented a steroid testing policy in March after allegations that a recent increase in home runs was due to players using performance-enhancing drugs.

"There couldn't have been a worse player to get nabbed, from our standpoint, than him," said one players' union source who spoke on the condition of anonymity. "And from his standpoint, it's baffling. Of everyone in the game, he had the most to lose."

Canseco wrote a book in which he stated that he injected Palmeiro with steroids while they were teammates in Texas, an allegation that Palmeiro strongly denied. Orioles owner Peter Angelos, a powerful Baltimore attorney, threatened to sue Canseco on Palmeiro's behalf after the book was published. Angelos issued a statement Monday reiterating his support for Palmeiro.

Staff writers Tarik El-Bashir, Thomas Boswell, Eli Saslow, Dave Sheinin and Rob Stein contributed to this report.

On July 15, Rafael Palmeiro became only the fourth player to have 500 home runs and 3,000 hits.