SACRAMENTO, CALIF. ? The U.S. Olympic track and field trials, always a scene of high drama and breathtaking triumph, begin today under a steroid-tainted cloud.

Maurice Greene — the Olympic champion at 100 meters, four-time world champion and self-proclaimed greatest sprinter ever — knows the drug scandal is an unavoidable topic, but he hopes performances can still shine through.

Four years ago, Greene felt the intense hype surrounding his 200-meter showdown with Michael Johnson, an event that fizzled when both runners pulled up because of injuries in the final.

This time, an uglier subject is dominating the headlines, and every athlete who does well in Sacramento knows there will be those who wonder if they are “clean” or not.

“It’s going to be very hard to convince someone that what you’re doing is pure because of all this negative talk,” Greene said. “I just tell them that I have a God-given talent, and I work very hard at what I do.”

Marion Jones will take the track in the 100 preliminaries today after weeks of vehemently denying that she ever used performance-enhancing drugs.

Tim Montgomery, her boyfriend and the father of her child, will run in the men’s 100 prelims on Saturday. He is one of four athletes in the meet under notice that they face lifetime bans from the sport for using performance-enhancing drugs.

Their cases are unprecedented, because none has tested positive. The allegations stem from circumstantial evidence gathered in the criminal investigation of the Bay Area Laboratory Co-Operative. Montgomery’s case is made worse by the leaking of his grand jury testimony to the San Francisco Chronicle, in which he is quoted as acknowledging he used performance-enhancing drugs — something he has publicly denied.

Greene and Montgomery are longtime rivals, the past and present world record-holders. Greene has called Montgomery “the luckiest man in the world” because his two fastest times, including his world record of 9.78 seconds, came with a 2.0 meters per second wind, the highest allowable for record purposes.

“Well, with the problems that he’s going through,” Greene said, “I think his luck ran out. I know he’s very stressed right now.”

Montgomery has only the sixth-fastest time by an American this year — 10.08. Shawn Crawford is the fastest, with a world-leading 9.88, followed by Greene’s 9.93 and John Capel’s 9.95. All three of those times came June 19 at the Prefontaine Classic in Eugene, Ore.

Jones’ last race also was at the Pre meet, where she finished fifth in the 100 behind winner Inger Miller. Jones still has the second-fastest time among U.S. women, 11.04. Still, the reigning Olympic gold medalist in the event — one of a record five medals she won in Sydney — is no shoo-in to make the team in the 100.

Greene said he sees flaws in her technique.

“I don’t know if it’s because she’s had a baby, but her running style has changed,” he said. “I think she has a lot more movement than she did before.”

Any unnecessary movement slows a sprinter, he said, and off-track distractions do the same.

“If you don’t have a clear mind when you’re going out on the track, you’re not 100 percent focused on what you do,” Greene said. “So most likely, you will not run the same type of races because you’re not totally tuned in to what you’re doing.”

Jones also will compete in the long jump and 200.

The women’s 100 semifinals and finals are Saturday. University of Miami senior-to-be Lauryn Williams has the fastest time in the field, and second-fastest in the world, 10.97. Others in the field include Chryste Gaines, one of the four facing lifetime bans if found guilty of steroid use despite no positive test.

The other two facing the charges are Michelle Collins, the 2003 world indoor 200 champion and one of the favorites in the women’s 400, and Alvin Harrison, the silver medalist at 400 meters in the 2000 Olympics.

The trials run though July 18, with a two-day break next week. The top three finishers in each event will be part of the U.S. team in Athens, provided they have met Olympic qualifying standards.

In addition to the women’s 100, there are preliminaries today in the men’s pole vault, women’s 100 hurdles and men’s shot put, among other events. Today’s lone final is in the men’s 10,000.

When the U.S. shot putters — so good they could sweep the medals in Athens — go to the infield today, one giant of a man will be missing. Kevin Toth, last year’s U.S. champion, will be absent. He has retired from the sport after testing positive for the designer steroid THG.

“It’s extremely frustrating as an athlete that goes out there on a daily basis to work hard and do it the right way with my own God-given ability,” shot putter Adam Nelson said, “that an athlete that I consider a peer and a friend makes a decision to do that simply because their own ego can’t stand that they are not good enough to compete at this level.”