Veteran California Rep. Robert Matsui (D), the head of the party’s fundraising committee and one of House Democrats’ most senior and knowledgeable Members on tax policy, died on New Year’s night of a rare blood disease. He was 63.

Matsui died at 10:10 p.m. Saturday at Bethesda Naval Hospital. According to his office, the Sacramento lawmaker had been suffering from Myelodysplastic Syndrome, a stem-cell ailment that prevents bone marrow from producing blood products such as red blood cells, white blood cells and platelets.

MDS can also lower immune systems and lead to a heightened susceptibility to other illnesses. Matsui was admitted to the hospital on Dec. 24 with pneumonia.

Very few people knew of Matsui’s illness.

For the last two years, Matsui held a leading post in the Caucus as chairman of the Democratic Congressional Campaign Committee. The long-time Member known more for his love of policy than of politics took on the job after much cajoling from Minority Leader Nancy Pelosi (D-Calif.), a personal friend and political ally.

Pelosi mourned the loss of Matsui on Sunday, calling him a dear friend, respected leader and dedicated family man. Matsui is survived by his wife, Doris; son, Brian; daughter-in-law, Amy; and granddaughter, Anna.

“In recent days, Bob spoke often of his parents, whose fortitude during his youth and grace during his adulthood shaped so much of his respect for America’s seniors and his resolve to preserve their retirement security,” Pelosi said in a statement. “With dignity, integrity and passion, Bob Matsui served his family, his community and his country. He will be sorely missed and long remembered.”

Doris Matsui said of her husband: “Bob wanted me to express his most profound gratitude to all of those he had the honor to serve and who made his life so extraordinary. Thank you to his constituents, his friends, his staff, and his colleagues. Brian, Amy, Anna and I will forever be grateful.”

Matsui was just elected to a 14th term in Congress. In addition to serving as chairman of the DCCC, Matsui was also the third most powerful Democrat on the Ways and Means Committee and ranking member of that panel’s the Social Security subcommittee.

A charitable fund is being set up in memory of Matsui, and friends and family ask that gifts be sent to The Matsui Foundation for Public Service, P.O. Box 1347, Sacramento, CA 95812. Memorial services have yet to be announced.

Matsui’s California colleague Rep. George Miller (D) called his friend “one of the toughest and most morally principled people in public service.

“His vision of fairness and principle for how to take care of the disadvantaged and poor was unparalleled in the political arena,” Miller said. “His vision of right and wrong always guided him in the complex and politically challenging policy fights in Congress over welfare reform, taxes, pensions, and Social Security, issues in which he was a recognized leader.”

Under California law, Gov. Arnold Schwarzenegger (R) has two weeks to decide when the election to fill Matsui’s 5th district will be held.

The special general election must be held on a Tuesday, no sooner than 112 days and no later than 119 days after Schwarzenegger officially declares the seat vacant.

An all-party special primary must be held on the eighth Tuesday before the date set for the general, according to the state’s election code.

If no candidate receives better than 50 percent of the vote in the primary, the top vote-getter of each qualified party advance to the special general election.

Matsui’s northern California seat is a Democratic stronghold were Republicans are not likely to seriously compete.

Chris Cillizza contributed to this report.