OSTON - From the halls of Congress and the streets of Boston, they came yesterday to the house that Joe Moakley built. Inside the grand new federal courthouse on the South Boston Waterfront, the popular congressman announced the beginning of the end of nearly five decades in politics.

The famous and not-so-famous were there, more than 100 in all, filling the jury assembly room of a courthouse that will undoubtedly be named for Moakley, who steered the project to the edge of his beloved neighborhood and fussed with bureaucrats over design features.

Against a backdrop of Boston Harbor, many cried as the 73-year-old warhorse said he has an incurable form of leukemia that prevents him from seeking a 16th term next year. At one point, Moakley choked up and paused to collect himself before completing a prepared statement and taking questions from the news media. But he often lightened the solemnity with his self-deprecating wit.

Initially, he believed his shortness of breath was caused by being “about 65 pounds overweight,” then he went in for a checkup that proved otherwise. “But I feel great,” he said, provoking laughs when he noted he has “yet to miss a meal or a night's sleep” since receiving the first bad news less than two weeks ago. The diagnosis was confirmed by test results Friday.

The South Boston Democrat suffers from “high-grade myelodysplastic syndrome that shows evidence of evolving into erythroleukemia,” according to a letter he released from his doctor, Brian P. Monahan, director of hematology and medical oncology at Bethesda Naval Medical Center outside Washington. “The condition is not reversible, and we do not have a means to cure it,” Monahan wrote.

Moakley, who has survived several other life-threatening ailments, said the prognosis “is not good,” but would not indicate his potential life expectancy. He reportedly has been told it is more likely a matter of months, not years, however.

“Despite today's headlines, I consider myself a very lucky guy,” Moakley said, calling his service a privilege. “The people I represent are more than constituents; they're family.

“I started in this business years ago as a bread-and-butter Democrat, and I stand before you today as a bread-and-butter Democrat,” he said to rousing applause from an assemblage that included Moakley's brothers, Thomas and Robert; Senators Edward M. Kennedy and John F. Kerry; and five House members from the Massachusetts delegation.

A tenacious inside player who has consistently delivered funding not only for the 9th Congressional District but also the entire state, he recounted some of his accomplishments, including the courthouse, the Big Dig, and the harbor cleanup. He is proudest, he said, of his work implicating the El Salvador military in the murder of six Jesuit priests in 1989, cutting off US military aid, and accelerating an end to the country's civil war.

“What else would you expect from a kid from South Boston?” Moakley said.

“And being an old-fashioned politician, I have also taken great pride in helping lots of folks find their lost Social Security checks, or help them get into a [Veterans Affairs Administration] hospital, or expedite student loans, or navigate their way through some federal bureaucracies,” Moakley said.

He vowed to fight as long as he can for what he believes in, including prescription drug coverage and a stabilization of Medicare funding “with that money GW [President George W. Bush] wants to give out in tax breaks.”

For the dean of the state's House delegation, the list of achievements and awards is long and impressive. But the honor Moakley has said he most cherishes is last year's Great Southie Reunion selection, with the late Cardinal Richard J. Cushing, as the most important South Bostonians of the last century.

When they name the courthouse for John Joseph Moakley and maybe a state building, too, (Governor Paul Cellucci, in Washington yesterday to receive an award, ordered aides to identify an appropriate state facility), it will memorialize an era in politics.

The Ward 7 Democratic ticket of 1952, when he ran for the Massachusetts House of Representatives, belongs in a museum of Bay State political memorabilia. Below Adlai Stevenson for president and Governor Paul Dever were John F. Kennedy for Senate, John W. McCormack of South Boston for Congress (later speaker), John E. Powers for state Senate (later president), state Representative Jimmy Condon and Moakley in the old double-seat House district, and Governor's Councilor Patrick “Sonny” McDonough.

Moakley, who went on to serve in the state Senate and Boston City Council before ousting another South Bostonian, Louise Day Hicks, from Congress in 1972, is the genuine article, among the last of the old breed. He is a direct stylistic descendant of two former US House speakers - McCormack (“almost a saint in my eyes,” Moakley once said), and Thomas P. O'Neill Jr., a close friend and mentor from Cambridge (“the epitome of what a man in public life should be,” Moakley said).

His low-tech politics are intensely personal and effective.

“He's helped me,” said Lisa Donovan, a waitress at South Boston's Galley Diner on P Street, where Moakley is a regular. A Moakley constituent from Dorchester's Neponset neighborhood, she said he has advised her on getting school services for her son, who has special needs.

Diner owner Paul Skudris said that most mornings Moakley fits in like just another customer, usually ordering Frosted Flakes, raisin toast, or a muffin. “No one bothers him until he finishes eating and reading the paper,” Skudris said. “Then, if someone has a problem, they'll talk to him.”

That's vintage Moakley, according to James P. McGovern, who was a Moakley aide for more than 13 years before winning his own congressional seat in 1996 in his native Worcester.

“Every time I walked into his office, he was on the phone doing casework, helping someone with a Social Security check or a problem paying the rent,” said McGovern, who considers Moakley “like my second father ... and my best friend.”

But McGovern also recalls traveling with Moakley to Santa Marta, a war-ravaged village in El Salvador in 1990, as part of his investigation. “He got up and started singing every Irish song he knew. People had no idea what he was doing, but they fell in love with him ... When we returned [in 1999] on the 10th anniversary of the murders, they had pictures of him all over, in the little huts or lean-tos. He was a hero to them.”

Moakley worked just as hard at pumping Uncle Sam's money into the local economy, to help “the two-dollar bettor, the average guy,” said Tommy McIntyre, a Bricklayers' Union official.

McIntyre recalled a conversation with Moakley 20 years ago about a federal courthouse Moakley wanted for South Boston.

“We were at the Gulfstream racetrack in Florida,” McIntyre said, “and I told him, ‘Joe, just make sure the ashtrays are made out of brick.’”

Today, the massive structure rises at the edge of the harbor, its veneer consisting of an estimated two million bricks.

“He's done a helluva job; nobody did it better,” McIntyre said. “As my mother used to say: They don't make 'em like that anymore.”