Harry R. Hughes, Democratic nominee for governor of Maryland, received the unanimous backing of the state's largest labor organization yesterday, an endorsement that means volunteer support and campaign contributions for the November election.

The political arm of Maryland's AFL-CIO endorsed Hughes over his Republican opponent, J. Glenn Beall Jr., who lobbied for the union's support. In the Democratic primary the AFL-CIO's Committee on Political Education backed one of Hughes' opponents.

The endorsement by the 370,000 member union's political committee was the first evidence that traditional bases of Democratic support would rally behind Hughes, a surprise winner in the Sept. 12 primary who underscores his preference for political independence.

"The people (of Maryland) wanted a change and we wanted to go with the people," said Nick Fornaro, state AFL-CIO president "Harry has always been good to labor. He's been out front on the issues."

While he served in the state senate in the 1970s, Hughes pleased labor with his sponsorship of Maryland's first graduated income tax. Later, as state transportation secretary, he developed a reputation for good labor management relations.

The AFL-CIO aids a favored candidate by sending newsletters with its endorsement to its large membership, providing volunteers for the routine work of campaigning and setting up a statewide telephone bank to canvass voters and encourage them to show up on election day.

A spokesman for Beall said the Republican nominee expects to attract a sizeable following among the AFL-CIO's rank-and-file despite the union's endorsement. "We're going to go after that vote," the spokesman said. "We feel our candidate reflects well on the problems affecting the working man."