SEATTLE — Longtime Democratic Rep. Jim McDermott of Washington state announced Monday that he will not seek re-election for a 15th time when he completes his term at the end of the year.

“I retire from the House forever humbled and grateful to my constituents for their unwavering embrace,” McDermott told reporters.

McDermott was first elected in 1988 and is the longest-serving member of the state’s congressional delegation. He has been re-elected by wide margins, and his seat is certain to stay in Democratic hands.

After telling his family about his retirement during his 79th birthday party Dec. 28, he said the first person he called was Democratic leader Nancy Pelosi, followed by his congressional colleagues and the people in the community who have counted on him through the years.

“I wanted them to know why I was leaving and that it wasn’t easy — this was not an easy decision to make, because I don’t like to quit,” he said. “There are things I still want to do, and I would still like to see happen, but there comes a time when you say to yourself: enough.”

President Barack Obama said McDermott “has worked tirelessly on behalf of the people of Washington state” and has been “a much-needed voice for his most vulnerable constituents.

“Across America, you’ll find families that are better off because Jim McDermott was fighting for them,” the president said.

Pelosi said in a statement that McDermott has been a “tenacious champion of hard-working Americans in Washington and across the United States.”

“Throughout all of his four decades of distinguished public service, Jim has shown the strength of his progressive values and the quality of his leadership in expanding opportunity for all Americans,” Pelosi said.

He declined to say whether he will back anyone to replace him, but said he hopes that person will be “progressive” and a good-listener. He said the voters in the 7th Congressional District, which includes most of Seattle and some surrounding suburbs, are “smart, thoughtful and careful,” and they should be allowed to take some time to decide who the best person will be.

Democratic state Rep. Brady Walkinshaw announced last month that he planned to challenge McDermott, saying he respected McDermott’s service but thought the area was ready for a change.

U.S. Sen. Patty Murray, D-Wash., said he’ll be sorely missed in Congress.

“Our state and our country are healthier, better educated, and more progressive because of Jim McDermott’s career dedicated to improving the lives of others,” she said in a statement.

U.S. Sen. Maria Cantwell, D-Wash., said she is proud to have fought alongside McDermott.

“From his service in the Navy to the state Legislature and the U.S. Congress, Jim dedicated his working life to making the Puget Sound, Washington state and our nation stronger and more prosperous,” Cantwell said in a statement.

McDermott said he was proud of the many things he has accomplished during his time in office, including reforms to foster care, affordable housing for people with AIDS, but most important, he said, was his work on the national health plan.

A psychiatrist, McDermott said he will spend the rest of the year working on a mental health reform bill. After he completes his term, he said he hopes to become a professor at a medical school, perhaps a dean. He also said he wants to travel more and do some painting.

McDermott is known for his liberal views and criticism of the Iraq war. He is a senior member of the tax-policy-writing House Ways and Means Committee.

McDermott has drawn attention, not always positive, for sparring with Republicans. He was involved in a long-running legal battle with former Rep. John Boehner, who would go on to become speaker, after leaking an illegally recorded phone call with Boehner and other GOP leaders. McDermott wound up paying Boehner more than $1 million in damages under a court order, but insisted he was defending the First Amendment.

In 2002, Republicans labeled McDermott “Baghdad Jim” for comments he made during a trip to Baghdad. He said Bush “would mislead the American people” to get the U.S. into a war in Iraq.

On Monday, McDermott said “I’m very proud of having said that and forcing many members of Congress to actually look at that issue.” The war “has turned out to be an unending disaster.”

“What we’re looking at today, 14 years later, is the result of the mistake we made by going in there,” he said. “Somebody had to say that stuff and this district gave me the power to do that.”

McDermott becomes the 31st House member to announce plans to retire or seek other office.