After a winter of arbitration and collusion hearings, of salary arguments and of the writing and rewriting of theoretical lineups, major league baseball gets down to the real thing this week.

Pitchers and catchers for 11 teams will begin spring training Thursday, and by Feb. 23 when the Toronto Blue Jays trot onto the field in Dunedin, Fla., all 26 clubs will be at work. Regulars are due a week later, and on March 3 the exhibition schedule will begin with the Chunichi Dragons and Los Angeles Dodgers playing in Vero Beach, Fla.

This month, players and coaches of the Baltimore Orioles have driven hundreds of miles to tell their fans that 1988 will be exciting, and that, if some of the young pitchers come around, if Pete Stanicek can adjust from the infield to the outfield . . . who knows?

Those words of incredible optimism come from a team that has lost 63 percent of its games since Aug. 5, 1986. The weirdest part is not that the Orioles say they might be a contending team, but that crazier things have happened, and are happening more often. Teams from Boston to Kansas City and from Philadelphia to San Francisco have been saying pretty much the same things, and who can argue?

If the game has proven anything the last three years, it's that time and champions fade quickly. It was General Manager John Schuerholz of the Kansas City Royals who celebrated the 1985 holiday season by giving his friends golf shirts with the words "World Champion Royals" above the left pocket.

"I wanted to do it this year," he said, "because you never know when you'll have the chance to wear it again."

His words rang true a few months later when the Royals plummeted from first place in 1985 to 10 games below .500 and 16 games out of first place in 1986. They aren't alone. In the last five seasons, 16 franchises have shared the 20 division championships, and in the National League it has been a decade since a team won back-to-back division championships over a full season. In fact, in the last decade all 12 National League teams have been involved in some kind of postseason play at least once.

Over that same period, 11 of the 14 American League teams have won something, with only the Seattle Mariners, Texas Rangers and Cleveland Indians having yet to throw a postseason party.

So excuse the world champion Minnesota Twins their celebration. Forgive them their Kirby Bears and their Kirby Pancakes and that they now have six players who'll earn at least $1 million in 1988.

It was a little more than three months ago the Twins were standing in the Rose Garden swapping jokes with President Reagan, having just completed an improbable season in which they were able to limp through a weak division with 85 victories, then rush past the Detroit Tigers in the American League playoffs and the St. Louis Cardinals in the World Series.

This winter, they've been toasted, roasted and saluted, and if history has proven anything it's that they'd better smoke their cigars now. Last season, only 10 games separated the seven AL West teams, and, although the Twins were unable to trade this winter, the second-place Royals and third-place Oakland Athletics both made dramatic moves.

The Royals, who finished two games behind Minnesota, added shortstop Kurt Stillwell, reliever Ted Power and left-handed pitcher Floyd Bannister. Those players fit nicely on a team with its stars -- center fielder Willie Wilson, first baseman George Brett and second baseman Frank White -- in their mid-30s.

"You don't know how many premier years they have left," Schuerholz said, "so our philosophy is that we have to go for it now."

But his changes have been minor compared to those made by the Athletics, a team that finished four games behind the Twins last year and should be so different that only third baseman Carney Lansford will be back where he was on opening day in 1987.

The A's needed pitching, and acquired Bob Welch and Matt Young from the Los Angeles Dodgers. Now, what was a weakness is a strength with a rotation of Dave Stewart, Welch, Storm Davis, Curt Young and either Matt Young or Rick Honeycutt.

They needed left-handed power to bat between right-handed-hitting Mark McGwire and Jose Canseco, and they acquired Dave Parker from the Cincinnati Reds. When they got him in December, they projected him to be a designated hitter, but when they came up an outfielder short they moved Parker to right and signed DH Don Baylor.

"We accomplished what all we expected," General Manager Sandy Alderson said. "From what we thought we could do when the season ended, we've probably gone a little further."

He accomplished so much that when he returned from baseball's winter meetings in December, the front office staff, led by Manager Tony La Russa, gave him a standing ovation. Yet, although the trades have been impressive enough, Alderson's rebuilding of the minor league system has laid a foundation for the next decade or so with a lineup that will include first baseman McGwire (24), left fielder Canseco (23), center fielder Stan Javier (22), shortstop Walt Weiss (24) and catcher Terry Steinbach (25).

Shifts in the National League appear less dramatic, with the New York Mets and the Cardinals again apparently head and shoulders above everyone else in the NL East. The Cardinals appear on course for another 95 or so victories. They lost slugger Jack Clark to free agency but added Bob Horner, who could be just as productive if he stays healthy. The Cardinals also added pitcher Jose DeLeon to a rotation that was already first-rate. Likewise, their bullpen and defense are as good as any team in any league.

But it would be hard not to pick the Mets, who won 92 games last season although pitchers Dwight Gooden, Ron Darling, Bob Ojeda, Rick Aguilera, Roger McDowell and David Cone all missed substantial time because of injuries or (in Gooden's case) drugs. They're all healthy this spring, but, even so, the Mets aren't invincible. Gary Carter hit .235, and Keith Hernandez struck out 100 times. Enter the Phillies?

The San Francisco Giants are again heavily favored to win the NL West. They went 51-32 after a Fourth of July trade with the San Diego Padres, and although the Los Angeles Dodgers have made dramatic changes the Giants appear more solid.

Likewise, the New York Yankees have made most of the noise in the AL East, having acquired Clark and pitchers Richard Dotson and John Candelaria. But as General Manager Pat Gillick of the Toronto Blue Jays said: "The Yankees are still short of pitching. I don't see them doing it, especially with the age of their pitching staff. I'm talking about Ron Guidry, Tommy John and John Candelaria. I just don't see them doing it."

In February, it's Gillick's Blue Jays that many people believe will win the AL East. But in February, it doesn't usually matter.