Charles W. Sandman, a New Jersey Superior Court judge and former United States Representative who was one of President Richard M. Nixon's strongest supporters during Congressional impeachment hearings in 1974, died Monday at Burdette Tomlin Memorial Hospital in Cape May Court House, N.J., after suffering a stroke Aug. 18.

He was 64 and lived in Erma Park, N.J.

The four-term Congressman from Cape May drew national attention as a staunch supporter of Mr. Nixon on the House Judiciary Committee during the last days of Watergate. As one after another of his Republican colleagues drew away from the President's cause, Mr. Sandman continued defending Mr. Nixon as a victim of partisan attack.

An ardent conservative known for a combative style, Mr. Sandman ran unsuccessfully for governor in 1973 on the theme he repeated throughout his career, a call for dismantling big government in favor of rule by local authority.

Became a Judge Last Year

Before that race, he had served from 1955 to 1965 in the State Senate - the last two years as president - and, since 1966, in the House of Representatives. Last year, Governor Kean appointed him to a seven-year term as a Superior Court judge and chief judge for Cape May County's family court.

''Charlie Sandman was a man of warmth, compassion and unfailing good humor,'' Mr. Kean said yesterday. ''But above all, he was a dedicated public servant who worked tirelessly toward improving the quality of life for all people.''

It was during the impeachment hearings in the House Judiciary Committee that Mr. Sandman briefly came into the nation's view: a heavyset man with glasses on the end of his nose, a pencil grasped between his hands, heaping sarcasm and scorn upon the arguments of those who would impeach the President.

''Isn't it amazing? Isn't it surprising? Isn't it astonishing,'' he said repeatedly, trying to point out inconsistencies in arguments of opponents.

A Prisoner of War

Mr. Sandman, the son of a milk-truck driver, was born in Philadelphia. He was reared in Cape May and graduated from Temple University and received a law degree from Rutgers.

Along the way, Mr. Sandman became a Golden Gloves boxer and served as an Army Air Corps navigator during World War II. Mr. Sandman's plane was shot down on his 23d birthday and he spent seven months as a prisoner of war in Germany.

His years in the House were marked by a voting record as conservative as the rural Second District he represented. He voted against busing to desegregate schools, against Federal revenue sharing with the states and against ending the House Internal Security Commitee.

Mr. Sandman ran for governor three times and the third time, in 1973, he won the Republican nomination. But he was defeated in the general election by Brendan T. Byrne in the most lopsided contest in New Jersey history, losing by 720,000 votes.

'Strict Construction' Believer

When public hearings to consider articles of impeachment against Mr. Nixon were begun by the Judiciary Committees's 38 members in the summer of 1974, Mr. Sandman, with Representatives David W. Dennis of Indiana and Charles E. Wiggins of California, led the defense of the President. Their strategy was to construe the evidence as narrowly as possible, require ironclad proof and propose benign explanations of information damaging to the President.

Througout, Mr. Sandman mustered particularly caustic remarks. But his position, he said, was based on legal principle, not emotions.

''My role is not one of defending the President - that's for sure,'' he said at one point. ''I believe in a strict construction of the Constitution. If somebody, for the first time in seven months, gives me something that is direct, I will vote to impeach.''

On Aug. 5, after Mr. Nixon released secret tapes of White House conversations and admitted he had ordered a halt to investigations of the Watergate break-in in 1972 for political reasons, Mr. Sandman, with other Republican Congressmen on the committee, reversed his position and supported impeachment. On Aug. 8 Mr. Nixon announced his resignation.

In his Congressional district the next fall, Mr. Sandman's support of the administration was the predominant issue of the campaign, and he was defeated by William J. Hughes, a former Cape May prosecutor.

Two months after the election, Mr. Sandman was appointed solicitor of Lower Township in Cape May and resumed practicing law.

He is survived by his wife, the former Marion Cooney; a sister, Edith Wallace of Erma, N.J.; four sons, William, Charles 3d and Richard, all of Erma Park, and Robert, of Mays Landing, N.J.; two daughters, Carol Wade and Marion Way, both of Erma Park, and eight grandchildren.

A funeral service will be held at Our Lady Star of the Sea Roman Catholic Church in Cape May on Thursday at 10 A.M.

Charles Sandman