State Sen. Tommie Broadwater Jr., a mainstay of the Prince George's County Democratic establishment and a leader of the black caucus in the Maryland legislature, was arrested yesterday and charged with conspiracy to traffic illegally in more than $50,000 worth of food stamps.

Broadwater was arrested just after noon at his legislative offices in Landover by agents of the U.S. Secret Service and the inspector general's office of the Agriculture Department. The arrest was one of five made yesterday as the result of a special 15-month Justice Department probe into food-stamp fraud.

Secret Service and Agriculture officials spent most of yesterday afternoon searching Broadwater's Glenarden home, his legislative offices and two of his businesses, the Chapel Oaks Farmers Market and the Ebony Inn in Fairmount Heights, in which he is part owner.

According to a joint announcement by the U.S. Attorneys for Maryland and the District, Broadwater was picked up after two of his associates yesterday were alleged to have bought about $25,000 worth of food stamps from a federal undercover agent and then given them to Broadwater in his legislative offices.

The officials alleged that Broadwater purchased the food stamps--and others worth a similar amount in the past--at a discount rate in order to redeem them from the federal government through his farmers market. Broadwater's two associates, William H. Dudley of Landover and Raymond (Jack) Quickly Jr. of Clinton, were also charged with conspiracy yesterday.

The federal charge carries a maximum penalty of $10,000 and five years in jail.

Broadwater, 41, was scheduled to be arraigned at 10 a.m. today in Baltimore before U.S. Magistrate Paul Rosenberg. Officials said that until the arraignment Broadwater would be spending the night in jail but they declined yesterday to say where.

Broadwater could not be reached for comment yesterday, and family members declined comment. Employes at the Ebony Inn said Broadwater had not been seen yesterday. They said Prince George's police and federal officers ordered everyone to leave the tavern at around noon and then searched the establishment for three hours.

Associates of the state senator reacted with astonishment when they heard of his arrest.

"You're kidding me," said Sen. Laurence Levitan (D-Montgomery), chairman of the Senate committee on which Broadwater was recently promoted to run a major subcommittee. "I'm sorry to hear that. I assume he'll be out on bail and I guess the question is whether the Senate has to act and what does this do to his schedule. He might want to be relieved of some of his duties."

Former Prince George's executive Winfield M. Kelly Jr., a close political ally and friend, said, "That's really sad. I didn't have any idea. Tommie's had a lot of problems, a really tough time."

Broadwater recently filed for bankruptcy, listing about $1 million in debts, including $25,000 owed to Kelly, $75,000 in back taxes to the Internal Revenue Service and smaller amounts to a host of friends and relatives.

At the time he filed for bankruptcy last January, Broadwater said he hoped his financial troubles would not "reflect in any way upon my political career or my associations with state and local officials."

Broadwater entered politics in a major way in 1974, running as the black candidate on the ticket of what was then one of the most powerful political organizations in Maryland--the Democratic organization forged by Steny H. Hoyer, now a congressman from Prince George's, and attorney Peter F. O'Malley. He won handily in his overwhelmingly black district.

A bail bondsman, Broadwater quickly earned a reputation at home and in Annapolis for his strident advocacy of black issues and for a life style that often appeared flamboyant and included showy clothes, cars and jewelry.

The latter, and Broadwater's lack of inroads among the county's growing black middle class, led to a political challenge in the 1978 elections when an opponent charged that Broadwater lacked sophistication and gave blacks a bad image.

Broadwater won that election but after that made a conscious effort to change his image, wearing conservative three-piece suits, abandoning a long Afro-style hair cut, and spending more time on substantive issues in the state legislature.

He also carefully positioned himself as the main spokesman for county blacks and principal dispenser of patronage in the black community. By 1980 he had built a strong political organization, providing important margins in political races from Congress to county executive. On occasion, he ran afoul of the law over mostly minor problems--failing to properly sign affidavits in his bail bond business and allowing nude dancing at the Ebony Inn.

After last fall's elections, Broadwater, who helped swing a black caucus vote to oust a conservative as president of the Senate, was given a new position of responsibility in Annapolis--chairman of a major subcommittee of the Senate Budget and Tax Committee. On the committee he has been the one consistent voter against recent budget cuts, saying that such reductions will only hurt "the poor and minority community."

Since the legislature convened in January, Broadwater has said he has been struggling to stay afloat in his businesses and with his new responsibilities in the legislature. But repeatedly he has said, "I'll make it, I'll make it. It's tough but I'm managing."

In a related investigation, federal agents also arrested two District men, William H. Johnson and John Frazier, who were charged with illegally buying food stamps and exchanging them for drugs and cash.

Officials in the office of District U.S. Attorney Stanley S. Harris said the food stamp fraud investigation began in the District and then spread to suburban Maryland, where it was directed by the office of Maryland U.S. Attorney J. Frederick Motz.