A smiling, balding man stepped onto an elevator at one of the World Bank's buildings here and stretched out his hand to a startled employe.

"Hi there, what's your name? My name's Barber Conable," said the president-designate of the bank, a former Republican congressman from upstate New York.

This geniality, unusual at the bank, may simply prove that politicians are compulsive hand-shakers. But Conable's boosters at the bank, where he takes over from A. W. (Tom) Clausen on July 1, believe that Conable's occasional but visible presence during the transition period already has been a morale booster.

"You know, they the bank staff haven't had that friendly one-on-one relationship, and I just know it will be so good for this institution," one official said. "If he comes up with the programs to match his natural, personal magnetism, then we've got a new ball game."

Staff morale will be an immediate, critical problem for Conable. Five years ago, the bank was accused by the Reagan administration of encouraging "socialism" rather than free enterprise. In the first Reagan term, the Treasury echoed Nixon Treasury secretary William Simon's view that "the bank is getting too big."

Then the administration turned full circle and assailed Clausen for not doing enough. It's also been charged that the bank has become a swollen bureaucracy, divided over the proper direction to take.

One staffer at the bank said Conable will have strong internal support for streamlining the operation. "There is an element within the bureaucracy that would welcome greater flexibility and efficiency," he said.

Conable has quietly taken one important step symbolic of the man and his style: He will not move into the handsome 12th floor presidential office used by Clausen, and earlier by Robert S. McNamara.

"That beautiful, pretentious, spacious office is not for me," Conable was quoted as telling a bank official. "It's too big -- I don't think I can think straight in an office that big."

Clausen's office will be turned into a lounge for visiting dignitaries, and a small board room nearby will be made into a more modest suite for Conable.

Former colleagues on the Hill say Conable is a politician of high principles. One rule he maintained through 10 successful election campaigns was a $50 limit on any contribution. ("I don't want to be owned," he explained when he retired from Congress in 1984.)

Universally, former colleagues praise his honesty and intellect. And among those who have worked for him, there is almost an unabashed hero worship.

American officials, anxious for the bank to play a larger role in solving the Third World debt crisis, are anxious for the new Conable administration to take over, anticipating that he not only will be more sensitive to American priorities, but to the tender and delicate business of extracting financial support for the bank group of institutions out of a suspicious Congress.

They assume that as an ex-congressman, Conable would have been more "understanding" than Clausen was last week, when he refused a Treasury request to delay a $500 million loan to Brazil to make its agriculture production more efficient. The administration feared it could increase competition for American farmers and cost some friendly farm support when bank appropriations come up for a vote on the Hill.

Bruce Bartlett of the American Heritage Foundation recalled that when former Treasury secretary Donald T. Regan early on made suggestions for changes at the bank, Clausen told Regan -- who represented the bank's biggest shareholder -- to remember that he was only one of many.

"Conable might think that, it's obvious," said a Conable intimate. "But I think he would say nothing. It's a place where no response at all is the best answer."

After 20 years on Capitol Hill, Conable has innumerable friends in Washington of all political persuasions. Two turned out to be crucially important in the decision that brought him the bank presidency: Vice President George Bush and Treasury Secretary James A. Baker III.

Bush and Conable sat together on the House Ways and Means Committee in the 1960s, and have been close ever since. In 1979, during the Bush campaign for the presidency, Baker was his manager and Conable his key spokesman in the House.

Conable has kept a low profile pending his actual takeover July 1. But those in the bank who have talked to him said they are impressed with his sense of confidence that he can do the job, even though he has had no experience managing anything larger than a handful of congressional staffers. The World Bank employs 6,000 persons.