When the government was gathering evidence to convict Baltimore Del. George Santoni of extortion last month, a covert FBI tape recorder picked up a Santoni comment destined to become one of those Maryland gems: "You can question my work; you can question my integrity; but don't you ever question my loyalty."

Loyalty, it has been said many times, is the political currency - "the coin of the realm" - in Maryland. It is still the measure by which most politicians judge each other in a state still dominated in many places by the clubhouse ethics Santoni summed up so concisely.

That is one reason the protest resignation last week of Maryland Secretary of Transportation Harry R. Hughes had such impact. That sort of thing just isn't done here.

The resignation is also one of several recent signals that outgoing Gov. Marvin Mandel - his administration and his machine tradition - are becoming a major focus of the 1978 wide-open gubernatorial campaign.

Hughes, a former state Democratic Party chairman and state Senate majority leader who would now like to run for statewide office, resigned because he said the process of awarding lucrative contracts in his department had been "tampered with" and "tainted" by prominent Baltimore contractor Victor Frenkil and Frenkil's vigorous lobbying for a piece of the $25 million Baltimore subway construction management contract.

The State Board of Public Works, run by Mandel, had at best tolerated Frenkil's meddling in a process set up in 1974 to prevent another Agnew-style kickback scandal. Or at least that is the implication of Hughes' allegations.

But Hughes worked for Mandel and to do what he did to the governor and the Mandel administration will inevitably be seen by roganization politicians as an act of profound disloyalty. "What Harry did - in politics - is tantamount to what Joe Valachi did in his business," said one experienced political operative.

"It's true," Hughes said. "There may not be room for someone who did what I did." Hughes said he was still deciding whether to run for an office in 1978.

What Hughes did will, in most any event, be an important part of the 1977 politicking for the 1978 Demoratic primary. It will be used against Louis L. Goldstein, a Frenkil associate who as comptroller sits with Mandel on the Board of Public Works and is running now for governor. It will be used against Lt. Gov. Blair Lee III, who is performing all of Mandel's duties, including defending the board, during the governor's two-month illness and upcoming corruption retrial.

It probably will be used against another gubernatorial candidate, Attorney General Francis B. Burch, who is a friend of Frenkil's as well.The only thing that could prevent it from being raised is that so many of the candidates seem to have some involvement with Frenkil that few of them will feel free to raise it.

In any case, it is another reminder that there will be a "Mandel issue," if not a Mandel presence in the campaign. But that was already becoming clear.

Lee was reasonably confronted with a decision as to whether he should openly accept the active support of political operatives so closely connected with Mandel that their support would clearly be a Mandel imprimatur.

One such operative is Maurice Wyatt, Mandel's chief patronage dispenser. From his style of dress to his savvy to his last name (one of Baltimore's most prominent political families), Wyatt symbolizes the younger generation of machine politics.

Mandel, according to one close associate, has repeatedly, but privately, expressed his belief that Lee is the most qualified candidate to replace Mandel. It is an opinion that may never be expressed publicly before the primary but it is enough to act as a signal to a Mandel loyalist like Wyatt.

Lee's use of operatives like Wyatt is already the cause for editorial needling by the Baltimore Sun and will be ammunition for opponents calling for a "breath of fresh air."

Lee was not about to reject Wyatt's support, however. "Maurice Wyatt is a sklilled political operator who I would not kick off for the sake of some editorial that would soon be forgotten," said Lee. . . . We've already had one governor who came in as a breath of fresh air," said Lee. "Spiro T. Agnew."

As a safeguard, however, Lee has nevertheless held exploratory ticketmaking discussions with the candidate most likely to be selling himself as an air freshener: Baltimore County Executive Ted Venetoulis.

Venetoulis, as 1971 campaign manager for Baltimore Mayor William Donald Schaefer, worked closely with Kovens who financed that campaign as well. Everybody knew that.

But in Venetoulis' own race for Baltimore County executive in 1974, he and his aides sought to convey the impression that Kovens was playing no role.

Two weeks ago, much to the relish of Venetoulis' opponents, the local Baltimore papers gave prominent play to stories that said that Kovens had indeed help Venetoulis raise money in 1974 although the amount - by Lovens' million-dollar standards - was token. Venetoulis was said to have been grateful that the issue was raised,, and he hopes disposed of, so early in the campaign.