"Linda Cropp?" I had to pull the phone receiver away from my ear. One of the city's big boys, an influential businessman who had gone all out to help land a major league baseball team for Washington, was on the line late yesterday, shouting. He could barely sputter the name of the D.C. Council chairman, the woman who may now be remembered as the architect of the most embarrassing, double-crossing act of treachery in this city's short history of home rule. "Linda Cropp?"

This executive, who didn't want his name in the same time zone as this column, couldn't fathom why the very same council chairman who just a few weeks ago stood beaming and waving while Mayor Anthony Williams announced that the Montreal Expos were coming to the District would now rip the rug out from under the deal with Major League Baseball. The Expos hadn't sold their first ticket when Cropp dropped a bomb that could mean the end of D.C. baseball before the first pitch is ever thrown.

No Anacostia riverfront stadium, Cropp says; build it instead near the RFK Stadium site. But Major League Baseball officials have made it clear they have zero interest in a site far from downtown.

Cropp's move mystified many. "I thought her whole game is that she's the voice of reason," another business type said, "the calm one who brings everyone together. How'd she get to be the bomb-thrower?"

Here's how: It's called politics. In this small city, with so few positions of power in a government vested with so little authority of its own, there is nothing more alluring to those who are in the game than the office of mayor. And even though the mayoral race is two years away, it's hard to talk to anyone in politics without getting a 20-minute lecture on the latest positioning and primping among the various potential contenders.

In the past couple of weeks, as a ragtag collection of opponents raised a stink about the mayor's proposal to have the city pay the whole freight for a baseball stadium in Southeast, it became apparent that most of the possible mayoral candidates were lining up against baseball.

The council's whiz kid, Adrian Fenty, came out hard and early against the deal. Council member David Catania had several near-cardiac moments as he raged against the new stadium at last week's public hearing. The outsiders gearing up for a mayoral run -- the recently ousted chairman of the D.C. Democratic Party, Scott Bolden, and boxing commissioner Michael Brown -- were letting it be known that they relished the chance to campaign against anyone who supported Williams's pricey stadium giveaway.

Cropp, according to two close friends who spoke with her at length about her decision, felt that if she was going to be a realistic contender for mayor, she had to move now to align herself with the anti-stadium feeling in town. And if that meant losing the Expos entirely, so be it.

"This is a great opening salvo for her campaign," said one of her close advisers. "Baseball is not dead. There's still 35 or 40 days to come up with a compromise package. Whatever the council decides Tuesday, they can go in a different direction in the final vote on Dec. 7."

But why would Cropp, whose stock in trade ever since she was on the school board in the 1980s has been her quiet, deliberative style, make this move without running her plan past the business leaders who had fought so hard to bring baseball back after three decades in the desert?

"Linda wasn't interested in talking to the mayor," another friend of hers said. "She knew where he was on this, and he wasn't moving. She had to take care of her own business." This friend, who has worked closely with Cropp throughout her years in city politics, said she was also eager to take a definitive, popular stance on this volatile issue before council member-elect Marion Barry begins to dominate the anti-stadium side, as she expects he will in the coming weeks.

It's a dangerous game Linda Cropp is playing. The lords of baseball play hardball on a much higher level than D.C. politics, and those guys own the ball. The Nationals may be ours for one season because baseball has nowhere else to put the team on such short notice. But if Cropp doesn't back off, that team is gone.