Maryland state Sen. Edward T. Conroy, 53, a Prince George's County Democrat who served in the state legislature for nearly 20 years and was an unsuccessful candidate for the U.S. Senate two years ago, died last night at Walter Reed Army Hospital where he had been under treatment for cancer.

It was announced last Thursday that Sen. Conroy, who had represented Bowie, Greenbelt and Upper Marlboro in the state Senate since 1967, would not seek reelection.

Sen. Conroy, a lawyer who maintained his own firm since 1960, was a highly decorated former Army officer who lost his left arm in the Korean War during the fighting at Heartbreak Ridge.

Throughout his political career he was known for his ties with and support of veterans' organizations. He was a past national commander of the Disabled American Veterans and held office in other veterans' groups. In 1966, he was named both Maryland's outstanding veteran and the outstanding disabled American veteran.

In the 1980 U.S. Senate race, Sen. Conroy waged a dogged and hard-fought but severely underfinanced campaign against the popular incumbent Charles McC. Mathias (R-Md.)

During that campaign Sen. Conroy showed himself as a vigorous advocate of a strong national defense and of increased defense spending. He also maintained his firm and longstanding opposition to federal funding of abortions.

Political observers labeled these stands as conservative positions, but Sen. Conroy was also recognized as a liberal on many other issues.

During a legislative career that began with election in 1962 to the Maryland House of Delegates, Sen. Conroy cast his vote for many human rights measures and won high marks from labor groups. He supported ratification by the Maryland legislature of the D.C. voting rights amendment

In the Maryland senate, where he was chairman of the constitutional and public law committee, he helped produce bills designed to promote open government meetings, broader consumer protection and greater ethics in government. He was known as an advocate of court and elections reform and equitable redistricting.

Sen. Conroy was born in New York and graduated in 1951 from Fordham University there. After college he was commissioned in the Army as a second lieutenant and sent to Korea where he won the silver star, the bronze star and two purple hearts.

After leaving the Army he enrolled at Georgetown University law school, where he received bachelor's and master's degrees.

One of the high points in Sen. Conroy's political career came on May 13, 1980, when he outpolled 11 opponents to win the Democratic nomination for the U.S. Senate. He defeated his closest rival by more than 20,000 votes.

A Bowie resident, Sen. Conroy amassed most of that margin in Prince George's County. He was defeated in the general election, however, by about 2 to 1.

Sen. Conroy also ran unsuccessfully in 1972 for the House of Representatives against then-incumbent Lawrence J. Hogan, and in December 1978, his quest for the presidency of the Maryland Senate ended in a hair's-breadth defeat.

Sen. Conroy left Annapolis in early April of this year--a few days before the end of the legislative session--to enter Walter Reed. He underwent surgery there April 15.

Survivors include his wife, Mary, of the home in Bowie, and two sons, Edward and Kevin.