It was early Monday night, four hours before the Maryland General Assembly was to adjourn for the year. On the first floor of the State House, legislators fumed and filibustered and threatened to scuttle much of the work they had done int he last three months.

On the second floor, the governor found himself alone in his office. He rose from his swivel chair, turned off the lights, strolled to a Victorian couch in the corner of the room and settled in for an hour-long nap.

This was the quintessential Harry Roe Hughes, a governor unlike any of his predecessors. At a time when others would have felt compelled to get into the middle of the action, to exert every ounce of power and authority, Hughes put his ego and his body to sleep.

There was no reason, Hughes said later,for him to do anything else. He already had spent much of the day conferring with the legislative leaders in an attempt to resolve the final-day deadlock and, when his catnap ended, he would spend the rest of the night doing the same thing in his own unobstrusive way.

From the day he took office in the middle of January to the final night of his first legislative session, Hughes seldom strayed from his conviction that the governor should not attempt to dominate the affairs of the General Assembly.

There were times during those first three months when Hughes seemed all but invisible.There were times when the legislators, who only a few years earlier begged for independent, now found themselves crying out for direction from the second floor. And there were times when the governor, who promised in his inaugural address that he would "act rather than react," seemed to be doing just the opposite.

But by the time the 1979 General Assembly session ended, it was clear that Gov. Hughes had accomplished most of what he had set out to do. His modest legislative agenda had been embraced and enacted; the government and the legislature were more often partners than adversaries.

For the first six weeks, Hughes was so detached from the day-to-day activities of the legislature that his office seemed like just another agency of the vase state bureaucracy. His aides monitored the status of bills on a computer, only occasionally taking a role in moving them them along. Rather thn impose his programs on the legislators, Hughes often relied on the General Assembly leadership to do the work, thus prompting some law-makers to call him "the me-too governor."

"In the early part of the sesson," said House Speaker Benjamin L. Cardin, "some members of the leadership felt the governor did not really have a plan of attack. Our initial meetings with him were more brainstorming sessions. He'd say,'Okay, fellas, whad daya want to do"'

About halfway through the session, however, Hughes realized that this new brand of executive restraint was eroding his position. The legislature appeared on the verge of shelving important parts of his tax relief package for its own versions.

"I started realizing," Hughes said in an interview today, "that if the program in which the governor was interested didn't get through, then the governor runs the risk of looking ineffective."

With his personal status on the line, Hughes began adopting a more forceful stance.

As an example of his new assertiveness, he asked legislative leaders to help him save face on a bill to eliminate the state sales tax on manufacturing equipment and farm manufacturing equipment and farm machinery. He introduced the measure as part of his tax package, but a House committee passed and sent to the floor an identical bill sponsored by a freshman Republican from Baltimore County.

Speaker Cardin recalls his reaction. "The governor," he said, "is as low key on pride of authorship as anybody I've seen in my life. But this one was a little too much for him to swallow. He said, 'You guys are going too far when I (Hughes) come up with the idea and you pass a freshman Republican's bill instead of mine.'"

The protest paid off for Hughes. House leaders sent the freshman's bill back to committee and made sure the administration bill took its place on the floor. "After that," said Cardin, "membership started realizing you better pay respect to administration bills."

As soon as Hughes assumed a more visible role in the legislative process, however, he faced a pardox. Many of the same legislators who had been complaining about a lack of direction from the second floor now were accusing the governor of suing strong arm tactics reminiscent of Marvin Mandel.

The first instnce of this came when Hughes and some of his aides lobbied vigorously to retain state funding for abortions for indigent women. When the antiabortionists learned that Hughes' patronage secretary, Louise Keelty, was taking part in the administration lobbying effort, they charged that the governor was attempting to trade jobs for votes.

This accusation, quickly retracted, brought an uncharacteristically sharp response from Hughes. "If that (bartering for votes) is the stronger method that's needed," he said, "Then you're going to have to find another governor sometimes to do that. It runs contrary to everything I have stood for, everything we are doing in this administration."

The charge arose again on the final day of the session when Sen. Julian Lapides (D-Baltimore) said that the governor's lobbying for a measure increasing the truck weight limit on state roads "gave me a deja vu of previous administrations." This time, however, Hughes seemed more amused than upset by the critism.

"This was the first session in many years that Jack (Lapides) waited until the day of the session to make a statement like that," said Hughes. "So that was an accomplishment all in itself."

Sometimes however, the governor found legislators less than responsive. One such instance came on the final day of the session when Hughes' secretary called to the Senate lounge to arrange a meeting for the governor with Sen. John J. Garrity, a Democrat from Prince George's County.

As Garrity was munching a doughnut and drinking his morning coffee, the Senate dookeeper rushed up and whispered, "the governor's office wants you to call right away."

The senator drained his coffee cup, strolled over to the phone and dialed the governor's office. "What does he want to see me about?" he asked the secretary.

"I don't know," came the reply.

"Well, ask him what he wants to speak to me about first, and then call me back," instructed Garrity, slamming down the phone.

Hughes' personal relationship with the legislators was as unusual as his professional one. Now and then he would walk down Main Street at day's end to mingle with the lawmakers at Fran O'Brien's restaurant or the bar at the Annapolis Hilton. With his unprepossessing bearing and sparse conversationl style, however, he seldom attracted much attention on these outings.

"I don't see any reason why they should treat me any different now than they did before I was governor," said Hughes. "I've sensed a warm feeling, but you know I don't believe in the crown system." CAPTION: Picture, GOV. HARRY R. HUGHES . . . low-key executive