The raucous, cheerleading fans who populate the upper deck behind the right field foul line at Baltimore's have a chant for the plate appearances of Gary Roenicke.

It probably will go "Rhi-no, Rhino."

Thus recognized, the 24-year-old left fielder will join the Orioles' other beloved sluggers - Ken Singleton, Lee May and Eddie Murray - who are greeted fondly during these days of Baltimore prosperity in the league standings.

Roenicke - known as "Rhino" to his teammates - quietly is establishing himself as a dominant force in the Oriole lineup.

His 14 home run total is one of the best marks in the American League. Roenicke's .275 average ranks him third only to May and Singleton among Oriole starters. His 37 RBI rank him fourth on the club.

But Manager Earl Weaver first cites another statistic when discussing Roenicke (pronounced rye-nicky). Going into the current road trip, he was third in the American League in on-base percentage (.444), trailing only Rod Carew and Roy Smalley, both of whom boast lofty batting averages.

In his first 176 at-bats his season, Roenicke drew 40 walks.

"He's got a good eye at the plate, more so than most guys his age," said Oriole hitting instructor Jim Frey. "His patience will get him ahead of a pitcher and then Gary can dictate which ball he will swing at.If the pitcher then doesn't give him good stuff, he's on base with a walk."

Roenicke also has reached base by stopping pitches with some part of his 6-foot-3, 203-pound anatomy.The right-hander stands scant inches from the batting box forwarding restraining line, often drawing inside pitches.

"I do that so I can reach the outside pitches," said Roenicke. "However, most of my home runs have been hit off inside pitches, so I guess I handle them pretty weel also."

Roenicke also has a new monicker - "The Man in the Iron Mask." That came courtesy of a high inside fast ball from Chicago's Lerrin LaGrow on the second day of the season. Roenicke was hit in the face, suffered a badly cut lip and was sidelined for 10 days. He now wears a double-bar football face guard on the left side of his batting helmet.

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Not retreating a single millimeter from his plate-crowding posture, Roenicke made opposing pitchers feel queasy as he went nine for 13 after the comeback. The Orioles soon afteward went on a 17-3 spree, fueled by Roenicke's seven homers during one 12-game span.

"You make a mistake to Roenicke and the ball is gone," said Kansas City Manager Whitey Herzog.

Roenicke has played a far different tune with his bat this season than in his disastrous debut in 1978 after being picked up from Montreal in a multi-player deal.

As a spot player. Roenicke hit badly (.194) in the first six weeks, and was shipped off to Rochester. There he had a torrid August and was recalled by the Orioles, for whom he remained hot in September and finished the season with a .250 major league average.

But coming into 1979 spring training Roenicke's status remained unclear in his own mind.

"Last season Weaver had taken me out when a right-hander pitched," Roenicke said. "I thought I might be platooned again this year."

However, Roenicke played himself into the regular lineup.

"Gary had always hit for a good average and, early last year, was just trying to survive," Frey said. "He was swinging for base hits. We tried to change his thinking and get him more conscious of swinging hard. Now he has gained that confidence. He can hit it as hard as anybody on the club.

"After he got the chance, Gary started hitting home runs off right-handers as well as lefties. He showed that he could do the job every day."