The request seemed ordinary enough: The dapperly dressed man who had rented the limousine simply asked his chauffeur to take him to the Watergate branch of the Riggs National Bank and wait outside.

But the instant the curious chauffeur peered into the bank, he knew the man he was waiting for was no ordinary customer. He quickly found a telephone and called his superior.

"He said, 'My client is robbing a bank,'" recalled the company official, who asked not to be identified. "We told him to get the hell out of there. That's all we needed is for a bank robber to use the car."

Last Friday, FBI agents arrested Jefferson Phillip Leatherman, 25, in New Rochelle, N.Y. and charged him in connection with the Sept. 24 attempted robbery of the Riggs branch. The FBI said Leatherman, who is being held in New Rochelle, has also been sought in connection with the $63,000 robbery last April of a California savings and loan.

According to the limousine company official, the man who on Sept. 24 rented the $38.75-an-hour car had become a frequent customer. Known to the company as J. P. Mann, he always paid in cash and never aroused any suspicions -- until his last ride, the company official said.

FBI agents said that the robber told the manager to take him to the vault or he would blow up the bank with explosives hidden inside his attache case, agents said.

However, the FBI said, when the manager explained that he could not immediately open the vault, the robber threw down his attache case and fled on foot. D.C. police bomb squad detectives later opened his case and found no explosives.

FBI agents say Leatherman had been in and out of Washington for several months before the attempted holdup here. During that time, agents allege, he made a $5,000 cash down payment on a 26-foot sailboat, created a company called "Universal Investments," and attempted to charter an amphibious plane to fly him out of Washington the day of the attempted bank robbery.

"He told us to meet him on the north side of the Key Bridge with the sea plane at 9 a.m. sharp," recalled Phil Platt of Calypso Airways of Easton, Md. "He said he'd be wearing a white hat and be sure to be there because it's very important," Platt said.

But Platt said he never showed up to pick up Leatherman: "It just sounded wrong."