TOKYO -- We'd better play it safe, thought the sponsors of a pro baseball game in Nagasaki last month. Buy some insurance. It's only 50 feet from the outfield fence to where the old folks play croquet. Who knows but a ball or two will crack some skulls out there?

Any Japanese would have had such worries. Bob (Red Devil) Horner, former Atlanta Braves third baseman, was coming to town. He sent one ball over the fence in his debut in Japanese pro ball on May 5. Three more followed in his second game. Two more came in his fourth game.

Japanese have been swept up in frenzied worship and wonder for "mammoth superman" Horner and his "stadium-exiting bullets." Fans grasp for his handshake. Mobs of photographers stalk him. Reporters study his minutest personal habits for clues to his baffling batting power -- his cowboy boots, gold chains and (reputed) ability to down two bottles of bourbon at a sitting.

He even is credited with reversing a nose dive in national morale caused by economic hard times. "I look forward to watching the news after work," says Tokiko Nishijima, a boutique clerk who roots for the Yomiuri Giants. "Even fans of opposing teams are delighted."

"A Horner wind is blowing across Japan," declared Sports Nippon newspaper. Kazuhiro Kiyohara and Hiromitsu Ochiai, two top Japanese sluggers, "appear now to be small. Pro baseball fans are talking only of Horner."

Happiest of all are the long-suffering loyalists of the Yakult Swallows, Horner's team and perennial bottom-rungers of the Japanese Central League. Now there is talk of the pennant, which the team has won only once, in 1978. Ticket sales have almost doubled and the stock of the team's owner, the Yakult soft drink conglomerate, is up.

Yakult products are sold door-to-door around Japan by 58,000 bicyle-peddling saleswomen. "Clients often ask them about baseball and Horner," says a team official.

Horner, who now has 10 homers and is batting .333, is handling his fame in a style the Japanese like: He appears stoic at the plate and has self-effacing praise for his team in the "hero interview" that often follows. "The bottom line is the team winning," he said recently. "If I hit a hundred home runs and the team doesn't win, so what? But if I hit 15 home runs and we win the championship, that's more important."

He is a rare bird, an American on the field in Japan at the peak of his career rather than its waning days. He is 29, a former National League rookie of the year (1978) who in nine seasons with the Braves batted .278 with 215 home runs and 652 RBI. In a game against the Philadelphia Phillies in July 1986, he hit four home runs.

He became a free agent Nov. 12. Earlier this year, he turned down the Braves' offers for contracts worth $4.5 million over three seasons and $3.9 million over two.

His deal here is said to be worth $1.3 million, plus living expenses, for one year, perhaps with $500,000 thrown in as a signing bonus. But Horner said it was baseball, not money, that brought him across the Pacific. "The Japanese called and made a good offer," he said. "I was at the point of thinking I was going to sit out the whole year."

The initial reception was not entirely friendly. The press unearthed stories about weight problems and drinking, vices that Japanese players are honor-bound to avoid, and in general do. Injuries were also cited. But they all became part of the lore with his barrage of home runs. (The feat comes easier here than in the United States; Japanese fields are a bit smaller.)

But he is not hitting balls out of the park as he did in his first few games. He did not hit his 10th until early June.

He blames the pitchers. "They're just pitching around me," he said. "You can only work with what you've got. I'm going to learn to have a lot of patience at the plate." But others see it as his own failings. In the June 2 game, for instance, he struck out each of his other three at-bats.

But a question also arises -- do the pitchers resent him as a foreigner? Japanese fans generally adore the batting power of imported gaijin (foreigner) players. But it leaves some baseball nationalists here fuming -- doesn't all this brawn undermine fine points of team spirit and cooperation on which the Japan's "unique" version of the game is meant to be based?

Things can come to a head when foreigners threaten to break records. A prime case came in 1985, when Randy Bass of the Hanshin Tigers was one short of tying Sadaharu Oh's single-season record of 55 home runs. By chance, in their last game of the season, the Tigers were up against Oh's Giants, with Oh looking on as team manager.

Bass was walked each of four times at bat. Some people said the Giants pitchers would have done the same for a Japanese, to save face for their master. Others saw it as a case of the Japanese banding together to protect one of their own.

"You can't take anything away from Sadaharu Oh," Horner said. "He's done some wonderful things and all credit goes to him. But at the same time, records are made to be broken."

The world of sumo wrestling is experiencing similar strains, as a quarter-ton Samoan American who fights under the name Konishiki moves toward top ranking. A cartoon in the Weekly Asahi magazine put Horner and Konishiki together singing a duet. "It's all through power that we are so strong. We're going to crush your silly strategies. We don't ever want to go home . . . "

Gaijin baseball players remain a restricted import item -- two to a team -- and periodically there is talk of barring them altogether. From the other side come pleas for full liberalization. If fans want more foreign players, argues sports columnist Takenori Emoto, let them have them.

Horner, meanwhile, is leading a life of hotels and travel made lonely by language and cultural barriers. Relations are cordial with fellow Swallows -- he saw "Platoon" with several one recent afternoon. But, as often happens with foreign players, close friendships do not seem to be in the offing.

Many evenings are spent with the Swallows' other American player, Leon Lee. "He's a godsend for me," says Horner. "He's saved me -- being able to go and talk to him, go out and have dinner. Being able to converse and get things off my back. You need that."

Horner visited Japan twice as a college player in the 1970s, and so had an idea of life here. But he can't have been prepared for the fuss he creates, even in his hotel lobby. "This morning, there were 30 reporters and photographers there when I came down," he said.