Sen. Henry M. (Scoop) Jackson (D-Wash.), one of the Senate's giants of liberal causes who was also known for his hawkish views on defense, died last night in Everett, Wash., after suffering a massive heart attack, according to city and county officials.

Jackson was 71 and had served in Congress more than 42 years, including 30 in the Senate.

The senator's death was confirmed by Willis Tucker, Snohomish County executive. County law enforcement officials said Jackson was "dead on arrival" at Providence Hospital after suffering a heart attack about a half hour earlier at his Everett home. Hospital press aide Diana Kempf said Jackson arrived there at 11:22 p.m. EDT.

Jackson's wife, Helen, arrived at the hospital with one of their two children shortly after midnight EDT, Kempf said. A short time later, Everett Mayor Bill Moore, a family friend, told radio station KIRO that Jackson "was gone."

A White House spokesman with President Reagan in Santa Barbara, Calif., said that the president was informed early today of Jackson's death. The president was "deeply saddened" by the news, and he expressed his sympathy for the family, the spokesman said. He said the president planned to telephone Jackson's family later today.

The ranking member of the Armed Services Committee and the third senior Democrat in the Senate, Jackson had twice tried for the Democratic presidential nomination, in 1972 and 1976.

A staunch supporter of U.S. involvement in Vietnam in the 1960s and '70s, Jackson was a particularly strong supporter of Israel. He authored the Jackson-Vanik Amendment, which was intended to cut off the Soviet Union's most-favored-nation trade status if it did not allow free emigration of Jews.

His powerful role in the American defense structure enabled Jackson to play an important part in arms control policy, extracting major concessions from the Nixon administration on the SALT I arms control agreement with the Soviets. He opposed the still-unratified SALT II pact.

But Jackson's was a guns-and-butter approach, and his stature was equally great as a leader of liberal causes, especially those relating to the environment. He wrote the Environmental Protection Act that created the Environmental Protection Agency.

In July, Jackson cast his 11,000th roll call vote as a senator and drew an ovation from his colleagues for the milestone.

"The nation has lost one of its best and wisest leaders," Senate Minority Leader Robert C. Byrd (D-W.Va.) said early this morning. "He was more than a colleague in the Senate. He was a counselor and friend. Henry Jackson was a national resource and he will be missed."

Born in Everett on May 31, 1912, the son of Norwegian immigrants, Jackson delivered newspapers while in school, earning him the nickname "Scoop." He attended Stanford University, then transferred to the University of Washington, working his way through both institutions. He received his law degree from the University of Washington Law School in 1935.

He was first elected to the House of Representatives in 1940, and served six terms there before defeating an incumbent senator in 1953 and taking a seat in the Senate. Jackson is survived by his wife and two children, Anna Marie and Peter Hardin.