Washington, March 3 (IANS/EFE): The Democratic Senator for Maryland, Barbara Mikulski, the woman who has served the longest in the US Congress, has announced her retirement after almost 40 years.

Mikulski, 78, entered the House of Representatives in 1977 from Baltimore and nine years later was voted to the Senate where she has been a fixture ever since, becoming one of the most influential lawmakers on the Democratic side of the aisle.

"This has been a hard decision to make. There's no health problem. I'm not frustrated with the Senate," she said at a press conference in Baltimore, where she announced her decision.

Mikulski said she would prefer to spend her last two years in office campaigning for the citizens of Maryland rather than campaigning for herself.

"I want to give 120 percent of my time focusing on my constituents," she said.

"Though I'm turning a new page, make no mistake, we're not writing the last chapter," the senator, known as a tough negotiator with a "booming" voice, said.

Between 2012 and 2014 she became the first woman to chair the Senate Appropriations Committee, one of the most powerful committees in the upper house.

US President Barack Obama said "Senator Mikulski is more than just a legendary senator for the people of Maryland, she's an institution in the US Senate".

"Barbara's service to the people of Maryland spans decades, but her legacy will span generations," Obama said.

In the 2010 elections, Mikulski won a landslide victory with 62 percent of the vote.