BALTIMORE -- The new ballpark in Camden Yards is being built rapidly. You can already see the girders for the third base grandstand. However, the team that will play there in 1992 is taking shape even more quickly. The Baltimore Orioles told their fans they'd have a contender in time to grace the old-fashioned-style jewel's first opening day. Now they might keep that promise a year early while they're in old Memorial Stadium.

"Thrilled . . . excited . . . really happy," were the bubbly words used by GM Roland Hemond and Manager Frank Robinson after the Orioles acquired one of baseball's best cleanup hitters, Glenn Davis, from the Houston Astros for Pete Harnisch, Curt Schilling and Steve Finley Thursday.

Evaluation: the best trade for the Orioles since they got Frank Robinson.

Hemond even draws the parallel comparison himself: "A bona fide cleanup man in a lineup makes a vast difference. I think you saw a guy show up in town in 1966 and make a big difference."

Glenn Davis isn't terribly famous -- unless you're a major league baseball player. Then the name pops eyebrows. Will Clark simply calls him the best power hitter in the National League. In a nutshell, think of him this way. He's Storm Davis's stepbrother with the same social conscience and self-discipline. On the field, he has, for six years, played first base and hit like the young Eddie Murray. And he's done it in the Astrodome. Nobody knows what he might do in a sensible hitter's ballpark.

At 6 feet 3, 210 pounds and 29 years old, he's a menace at his peak. Playing in the Orioles' high-on-base percentage lineup and in cozy American League parks, you can write Davis down for 30 homers and 100 RBI right now. He's had only one injury (last year) and averaged 31 homers and 96 RBI in his four full years from '86 through '89.

Most important, the Orioles got him without giving up anybody they can't replace immediately from within their own roster or farm system. That's why you build an entire deep organization. The Astros were holding a cut-the-payroll discount sale (as owner John McMullen tries to sell the team), and the Orioles stepped in. They had more decent young players to offer than any other team. Any team would want a Davis, but only the California Angels, offering Wally Joyner, plus others, could compete.

"I think we're right there with anybody in our division now," said Robinson, "and we can play with anybody in our league. We were pretty close last year. We have really helped ourselves. Now, it's just a matter of performing."

"I said after the season that we needed to add two quality offensive players. In Davis and {free agent Dwight} Evans, we have," said Robinson. "This means a lot for Cal Ripken and Randy Milligan. It takes the pressure off them. The last couple of years, Cal felt, 'If I don't do it, it's not going to get done.' Now, he can just be himself. It helps the whole lineup."

The Orioles must be excused if they feel and act a little giddy. This trade, weeks in the making, was enormously important for them to complete. Nowhere in their organization did they have a legitimate cleanup slugger, although they had almost everything else. Now, they have, as Hemond says, "traded from our surplus."

With Evans's back apparently healthy, Robinson would love to play the 39-year-old, who is the game's active home run leader, in the outfield as often as possible. Removing Finley unclogs the picture.

Also, the Orioles have so many interchangeable pitching prospects -- the names fall off Hemond's tongue like a mantra, "Mesa, Telford, Myers, Rhodes, Mussina" -- that it seems probable that pitchers of Harnisch's solid but unspectacular level will not be in short supply. As for Schilling, his good-arm-bad-head reputation made him expendable with Mark Williamson returning as set-up man in the bullpen.

Hemond made this trade, but it bears the stamp of Doug Melvin, the player personnel guru whose strong prospects made it possible. "This is baseball," Melvin said yesterday, grinning like a kid. "Of all the names of hitters that we mentioned in trades or as free agents -- Cory Snyder, Danny Tartabull, Candy Maldonado, Franklin Stubbs -- we came up with the best, by far. . . . Earl Weaver might like our lineup now -- we've got some three-run homers."

As the Orioles look around, they wonder who is better in the AL East. The Blue Jays have lost George Bell and probably got the worst of the Fernandez-McGriff for Carter-Alomar trade. Toronto's day seems past. The Red Sox got Jack Clark, a fine hitter when healthy but a very disruptive clubhouse force everywhere he's been; however, they lost 17-game winner Mike Boddicker. Overall, a minus.

The only person as enthusiastic as the Orioles brass was Davis himself. "I'm excited . . . I didn't know about this {trade being in the works}. It's all new to me," he said by phone from Houston. "I want to be part of a contender. I am very happy to be a key part of building this club.

"Storm had very good things to say about Baltimore. It's nice to be with somebody out there who wants me. . . . Baltimore was the first team that drafted me out of high school and the first team I put on a professional uniform with. I decided to go to college instead of going pro, but the Orioles uniform was still the first one I ever wore when I worked out at Bluefield."

In Davis, the Orioles know exactly what sort of person they are getting -- the best. Last year the first Bart Giamatti Award ever given went to Cal Ripken Jr. as the sport's model citizen. Next week, the second Giamatti Award will be given to Glenn Davis, who, among other things, has founded the Glenn Davis Home for Boys.

If all this sounds too good to be true, it is. There's a fly in the ointment. Maybe.

Davis will be a free agent after 1991. Will the Orioles and owner Eli Jacobs be able or willing to meet the sport's existing salary structure?

If Davis performs as he always has, then he will be the litmus test for Jacobs's pocketbook and his popularity.

It's unlikely that any negotiations will be completed before Opening Day. Team president Larry Lucchino says talks will begin immediately but at an unhurried pace. However, sometime between Opening Day and the All-Star Game, the Orioles will certainly have to get serious about a contract for Davis that will make him part of Camden Yards. Star players who aren't signed before the dog days of summer are seldom around the next year.

But if Jacobs won't pay the price, then fans may just tear down the new park with their bare hands before the team ever plays there. Why shouldn't they? Their tax money is building it.