BACKSTAIRS MANEUVERING over state contracts is, sadly, nothing new in Maryland. What is unusual, though, is for a top state official to resign in protest, as Transportation Secretary Harry R. Hughes has just done. Mr. Hughes says that the process of choosing a management contractor for the Baltimore subway line has been "tampered with and thereby tainted." By bluntly attacking prominent Baltimore contractor Victor Frenkil and the state Board of Public Works - which consists of Gov. Marvin Mandel, Comptroller Louis L. Goldstein and Treasurer William S. James - Mr. Hughes is also laying on the line his own considerable reputation for integrity and managerial competence. His own role in this case, as well as everyone else's, is bound to be closely scrutinized - especially if, as is widely suggested, he is thinking of running as an anti-corruption candidate for governor next year.

Whatever Mr. Hughes' motives or intentions may be, the record so far shows ample cause for him - and Maryland taxpayers - to be frustrated and concerned. In the wake of earlier scandals, students of Maryland public administration will recall, the state in 1974 set up a professional selection board and procedures to take politics out of the contract-awarding processes. In accord with that system, Mr. Hughes' department last year chose a consortium headed by the Ralph M. Parsons Company of California as best qualified for the $25-million-or-so job of managing the subway project, the largest public-works undertaking in the state's history. Out of five finalists, Mr. Frenkil's team was rated as least qualified.

Under both state and federal rules for such contracts, the state should have proceeded to work out detials with the Parsons group or else turned to the second-rated firm. But Mr. Frenkil, an immensely audacious and pugnacious man, did not stand still for that approach. While pressuring the Parsons company to let him climb aboard, Mr. Frenkil began advancing a lower-priced plan before the Board of Public Works. In November Messrs. Mandel, Goldstein and James decided not to approve the Parsons bid. Ever since, they have been looking for ways to redefine the contract and reopen the competition among all five firms.

Mr. Hughes is not the only to take a dim view of this maneuvering. The federal mass transit agency (UMTA) has consistently warned the state not to try to circumvent the rules. In an April 21 letter that noted, "We do not understand why Parsons was not approved," UMTA told the state to either deal with Parsons or propose new rules. The letter also noted that if the subway is delayed by the state's stalling, the federal government will not help pay the extra cost.

And there things continue to boil. While the extent of actual improprieties is not yet clear, it surely looks funny - and all too familiar, as if the much-touted reforms in Maryland government were really just for show. With the state's top elected officials up to their elbows in the mess, it's little wonder that Mr. Hughes, who seems to take the new rules seriously, got fed up and got out. Perhaps the next election will bring changes. Meanwhile, once again it seems to be left to federal agencies - UMTA and the GAO, which is investigating - to crack down on unsavory dealings in Maryland.