''Any Senator who stays out of jail or a detox center is a contender for the White House,'' Sen. John McCain, R-Ariz., once said. But Senators--even respected Senators with strong legislative records--usually make terrible presidential candidates. They run, they raise millions of dollars, and they get humiliated at the polls.

It's not so hard to figure out why they run. Every member of the chamber is ambitious. And the presidency is the next step up. Look at the roster of Senators who seriously considered running in 2000: Paul Wellstone, Bob Kerrey, and John F. Kerry on the Democratic side; for the Republicans, John Ashcroft and Fred D. Thompson. They all looked at the record and said no.

Remember Edmund Muskie? He looked like Lincoln in 1970. He looked like cold toast in 1972. In 1984, John Glenn was supposed to have ''the right stuff.'' And he did. But not for President. Arlen Specter didn't even make it to the first contest in 1996. Phil Gramm did. After losing the Louisiana caucuses to Pat Buchanan, Gramm said that ''there are going to be three tickets out of Iowa. We hope we're going to get one of those tickets.'' He got a ticket out of Iowa all right, but not to the destination he wanted. Joseph R. Biden Jr. ran into a buzz saw in the 1988 campaign after it was pointed out that his stump speech sounded a lot like a speech delivered by a British Labor Party figure. Bob Dole decided he had to leave the chamber to become a credible presidential candidate. It was probably the finest moment of his entire campaign. ''I will stand before you without office or authority,'' he said in May 1996, ''a private citizen, a Kansan, an American, just a man.'' Dole's legacy? One of the country's greatest Senators. And one of its worst presidential candidates.

Like Dole, Bill Bradley decided to run as a former Senator. Bradley left the chamber four years early, however, to give himself time to retool his image. He's now running as a Washington outsider. And doing pretty well.

Look at what happened to once-and-still obscure Bob Smith this year. On Feb. 18, he got into the Republican race. On July 13, he checked out of the Republican Party but stayed in the race. Last month, Smith got out of the race and returned to the GOP fold. ''Bob, welcome back,'' said Senate Majority Leader Trent Lott, who promptly rewarded Smith with the chairmanship of a major committee.

A few Senators have escaped presidential politics fairly unscathed: Henry ''Scoop'' Jackson in 1976, Howard Baker in 1980, Alan Cranston and Ernest F. Hollings in 1984, Paul Simon in 1988, Bob Kerrey and Tom Harkin in 1992.

John F. Kennedy is the model--and the last time a Senator went directly from Capitol Hill to the White House. But Kennedy, who served only one full term in the upper chamber, was never a man of the Senate. He didn't base his appeal on legislative effectiveness. He based it on an idea: a new generation of Americans coming to power.

When his brother Ted tried to become President 20 years later, it didn't work out as well. The idea behind Ted Kennedy's candidacy wasn't too clear. It was only after his failed presidential campaign that the younger Kennedy became a man of the Senate, one of the country's most respected legislators.

Only a few Senators have managed to have an impact on their parties despite losing a presidential race. Gary Hart did after his first race in 1984 when he ran, not on his legislative record, but on his ideas--make that new ideas. Barry Goldwater's campaign also failed, but his ideas reshaped the Republican Party. Eugene McCarthy and George McGovern did the same thing on the Democratic side. Goldwater, McCarthy, McGovern, and Hart had one thing in common--they all ran against their party establishments. That's not easy for Senators who have pursued successful legislative careers. An influential and prestigious Senator is by definition a member of his party's establishment.

Two Senators are left in the 2000 presidential race. One of them is running on his stature in the chamber. ''I have the most experience of anybody in the race,'' Orrin G. Hatch has said. ''I've got a better record of accomplishment than anybody in either party.'' It doesn't look good for Sen. Hatch.

The other is running as an outsider, someone who challenges the rules and doesn't get along too well with his colleagues. John McCain has even become the target of a ''whispering campaign'' by his fellow Senators, including leaders of his own party. They are reported to have suggested that McCain's years as a prisoner of war in North Vietnam left him mentally unstable. ''I have not been voted 'Mr. ongeniality' for the 13th straight year in the Senate,'' McCain says with some pride. ''I've got to do what's right.'' The latest CNN-Time magazine poll shows McCain edging George W. Bush, 37 percent to 35 percent, in New Hampshire.

The skills you need to be an effective Senator-- especially the knack for being a hard-nosed wheeler and dealer-- are simply not very attractive in a presidential candidate. But there's another way Senators can get to the White House--become Vice President. A lot of Senators have been named to their party's ticket--Richard Nixon, Lyndon Johnson, Hubert Humphrey, Walter Mondale, Al Gore--and landed in the VP's suite. Now that's a jump that can change an ex-Senator's image--even though it doesn't always get him elected President.