Call him Senator Stamina. When he's taking it easy, he'll leave Capitol Hill at 2 or 3 in the morning. Then It's a refreshing three or four hours of sleep before returning to his office.

One legend has it that Hawaii's junior Democratic senator, Spark Matsunaga, works skewed hours because of the five-hour time difference between Washington and Honolulu. Not so. He works long enough to embrace the business hours of both capital cities' time zones because millionaire industrialist Henry J. Kaiser once shared with Matsunaga -- then a young territorial legislator -- his recipe for success.

"Ever since my 28th birthday," the founder of Kaiser Aluminum told Matsunaga 25 years ago, "I've never slept more than four hours a day . . . If you value your life, value your time, for time is the stuff life is made of."

Today the 63-year-old senator says that's why he works the 14-day shifts that drove his Republican predecessor, Hiram Fong, to retire in 1976. The former boxer, Matsunaga says a half-hour of calisthenics in the morning and evening -- including a bout with a punching bag in the basement of his Kensington home -- keeps him trim.

"He's an indestructible, emergetic sort of person," vouches Bill Cochrane, chief counsel to the Senate Rules Committee. Until Matsunaga came along, Cochrane was Mr. Late Night, but Cochrane says when he leaves work at 2 a.m., Matsunaga's car is still in the Senate garage -- on weekends, too.

"I think maybe I'm too much of a perfectionist, maybe it's a fault," says Matsunaga, who insists on reading every letter that goes out from his office. That's a duty many other legislators delegate to their staff's. Another time-consuming habit Matsunaga has acquired: taking constituents to lunch. Every day. Several thousand a year. His annual luch tab: about $15,000.

The Federal Election Commission and the Senate ethics committee ruled Matsunaga may use campaign funds for those lunches as long as he intends to seek reelection. But the senator says the lunches he hosts daily at the largest table in the Senate dining room are more than savvy politicking.

"When I was in my second year in the House, there was an elderly couple from Maui of native Hawaiian ancestory," Matsunaga says. "The husband had just retired after 40 years with the Maui Pineapple Company, and the first place he wanted to visit was Washington."

Matsunaga says the couple had never left Hawaii, and a neighbor called to ask that he give them a few moments of his time. Matsunaga feted them, guided them around the Capitol and when he shook their hands in farewell, the man said, "Sparky, you know I work for Maui Pineapple 40 years. And 40 years I pay Uncle Sam taxes, and he no give me back nothing. But I no grumble. Uncle Sam today pay me all back." g

That convinced Matsunaga he had a hit program on his hands, so today he's well known as the senator who is happy to walk constituents around the Capitol before tying on the feedbag in the Senate dining room. A few weeks ago there tables in the dining room were filled with Matsunaga constituents. The senator had soup at one table, the main dish at another and dessert at the third. Then he picked up the tab and returned to his office for the last 12 hours of his workday.