BALTIMORE -- How else can the rookie-year exploits of Kevin Maas be described except as positively Ruthian?

Yet even that most glowing of baseball superlatives fails to do justice to the virtually unprecedented beginning of Maas, for it was not until Babe Ruth's second season of playing the outfield that the Sultan gained his full measure of swat.

With each new unfurling of his potent left-handed swing, Maas threatens another record for productivity and prompts comparisons, however premature, to the game's all-time home run kings.

None of history's leading power hitters -- not Ruth, not Hank Aaron or Willie Mays or Frank Robinson -- had the immediate impact of the 25-year-old Maas, the New York Yankees' first baseman since back troubles began bothering Don Mattingly two months ago. Maas began tearing through the American League shortly after his June 28 promotion from Class AAA Columbus, and he hasn't relented. He has 15 homers, most of them gargantuan, in 162 at-bats.

That's a home run nearly every 11 at-bats; Ruth is the most efficient of those on baseball's top 20 homer list, with one for every 11.8 at-bats. And while no one in a Yankees uniform -- including the unassuming Maas -- is issuing guarantees of a 500 home run career, the early returns certainly serve to spark the imagination.

"That I've hit for some power isn't surprising," Maas said in the visitor's clubhouse at Memorial Stadium this week. "How fast I've been able to do what I've done is a little surprising."

The Yankees have been pleasantly shocked. New York officials thought they had an all-fields hitter with power potential when they called upon Maas to take over for Mattingly. What they've gotten is a homer terror who has learned to adapt his stroke to the short right field porch in Yankee Stadium -- where Maas has nine home runs in 62 at-bats -- and has turned most mistakes from pitchers into distant souvenirs.

"He was not a dead-pull hitter when he came up," Yankees batting coach Darrell Evans said. "He has the ability to spray the ball around. . . . But he also has the ability to hit some long balls, and to take advantage of home run potential in Yankee Stadium. A left-handed hitter has to pull his fair share of balls."

So Maas opened his stance a bit and made a concerted effort in the first few weeks of his Yankees tenure to yank the ball to right. The result, as Evans phrases it, has been "the creation of a monster." Fast-Paced Start

Maas's first major league home run came in his 15th at-bat, July 4 off Kansas City's Bret Saberhagen at spacious Royals Stadium. His second homer came in his 21st at-bat, and three more followed in Nos. 26, 27 and 28.

Maas reached 10 home runs faster than any other player in major league history -- in his first 77 at-bats, surpassing by two the record held by Boston's George Scott. He got to 13 homers in a record 110 at-bats (topping Sam Horn's old mark by 13 at-bats) and to 15 in a record 133.

He tied Texas's Dave Hostetler for the most home runs (12) in his first 100 big league at-bats. He has the most homers for a Yankees rookie since Bobby Murcer hit 26 in 1969, and trails only Atlanta's Dave Justice -- by five home runs -- among major league first-year players. His longest homer drought is the 29-at-bat skid he has after last night's game against the Orioles at Memorial Stadium.

Few of his home runs have been cheap. By his estimation, only one of his Yankee Stadium homers came on a drive that wouldn't have been out of the majority of major league ballparks. Maas has been a frequent contributor to the late-night television highlight reels, with a succession of blasts resembling the 450-foot rocket shot off Seattle's Erik Hanson three weeks ago that made him the 21st player to reach the Kingdome's upper deck.

"When he hits them, there's no doubt," said New York Manager Stump Merrill, a 14-year organization man who also managed Maas at Class AA Albany in 1988. "He's an exciting kid. . . . We've got some kids here to build around, and he's certainly one of them." Mostly Humble Beginnings

Maas was not always a prodigy, however. In fact, he usually has been more blue collar than blue chip. His 6-foot-3, 205-pound frame hints at pure athleticism, but not raw power. The lone physical clues to his long-ball proclivity are his barrel chest and well-muscled arms.

He was selected by the Yankees in the 22nd round of the 1986 amateur draft out of the University of California-Berkeley, and he progressed through the New York organization regarded as a prospect, not necessarily a sure thing.

"If Donnie hadn't gotten hurt, he'd probably still be in the minors," Evans said. Maas's road to the majors gave only an uncertain indication of the torrid start he'd craft once he arrived. He hit 28 home runs in 480 at-bats during a 1988 season split between Class A Prince William and Albany, but he managed just six homers in 83 games during an injury-marred campaign last year at Columbus.

Maas underwent arthroscopic surgery on his right knee in August 1989, prompting the Yankees to remove him from their 40-man major league roster before spring training. He reported to minor league spring training, and his goal for this season was to receive a big league callup when the rosters expand Sept. 1, and perhaps catch enough eyes to have a chance to make the club in 1991.

"I had always gone one level, one year at a time," said Maas, who has 29 RBI in 50 games. "My sights were set toward having a good year at Columbus and getting up here in September. After that, I really didn't worry about it." Taste of Stardom

He is personable and engaging despite the mostly unwanted onslaught of attention. He returned to school during offseasons to earn his mechanical engineering degree, and his conversations are full of allusions to a deeply religious backround.

He says he'd prefer to go about his business quietly and unnoticed but realizes that no longer is possible. His best friend is his brother, Jason, an outfielder in the Yankees' organization with whom he roomed for three years in the minors.

If not for Jason signing with New York a year before he did, in fact, Maas -- an Oakland Athletics fan throughout his Bay Area upbringing -- may have returned to school when the Yankees chose him.

"The Yankees may have been the only team that could've signed me at the time," he said. "Maybe Oakland too but the attraction of being a New York Yankee is very strong."

Maas, as a rookie without a large reputation, was insulated from the George Steinbrenner fiasco that was taking place as he broke in. The Yankees have stabilized -- winning 21 of their last 34 games -- as he has flourished, and Maas has done his best to take the overwhelming developments in stride.

He shrugs at the ceaseless praise. He defers to Merrill's judgment when asked about the Yankees' problem when Mattingly is ready to return to full-time duty, a recovery that probably will not be complete until next season. (New York officials say they'll move one to the outfield, although they're not yet sure which one; Maas was mainly an outfielder in the minors).

Maas is recognized at restaurants and movie theaters in New York City these days, and he allows that "sometimes {the notoriety} is nice because you don't want to wait in lines." He has yet to conduct a noteworthy battle with the New York media, and his ego appears in check.

"I see myself as someone who came up and helped the team when we needed it," Maas said.

His legend among opponents is growing by word of mouth from his batting-practice power exhibitions and by TV viewing. "I've never seen him play in person before, but I know all about him from watching some of those tape-measure homers on ESPN," Orioles pitcher Ben McDonald said before starting against the Yankees Monday.

Said Merrill: "He's the kind of kid you like to see good things happen to. You worry about a kid getting a big head from something like this, but he remains very level. I guess he won't keep up a pace like this, but he should be a very consistent home run hitter for a lot of years."

HOME RUN RECORDS

10 in first 77 at-bats in majors: Old record, 10 in 79, George Scott, Boston, 1966.

12 in first 100: Ties Dave Hostetler, Texas, 1982.

13 in first 110: Old record, 13 in 123, Sam Horn, Boston, 1987.

15 in first 133: Old record, 15 in 135, Wally Berger, Boston, 1930.