When he entered the elegant chamber, attired as usual in subdued gray, the crowd responded with polite applause. But by the time he left, Maryland's shy and retiring governor had General Assembly legislators cheering in the aisles, slapping him on the back, declaiming against Ronald Reagan--and proclaiming among themselves the birth of a new, more political Harry Hughes.

There was nothing typical about the State of the State message that the normally cautious Hughes delivered here today. From the outset, he startled legislators by announcing that he would put aside his prepared remarks, forgoing the traditional, dry recitation of past accomplishments. Then he unleashed a partisan political stemwinder, telling "what one man feels," condemning Reagan's fiscal and social policies and saluting Maryland, particularly under his administration, as a model, Democratic alternative.

"It's cold out there, Mr. President," Hughes cried out, speaking to Reagan on the first anniversary of the Republican's inauguration, as well as to the General Assembly. "But this is one state that is ready to handle the weather. We're going to find ways, Maryland ways, to do a better job than we've ever done before."

The governor's voice rose and fell like that of an evangelist or a stump campaigner, and in fact the speech appeared to be the opening shot of his 1982 reelection campaign. Among those who helped write it was longtime Republican media consultant Robert Goodman of Baltimore, Hughes' neighbor and friend who is working for the campaign.

Leaders of the lopsidedly Democratic legislature--who have long urged Hughes to scrap his apolitical style, to speak more as a partisan Democrat and to attack Reagan--beamed throughout the 15-minute speech. When it was over, the crowd applauded for 46 seconds, a standing ovation complete with cheers and whistles that was such a contrast to the tepid reception Hughes often receives from the legislature.

"Great speech, governor. I'm very proud," bubbled state Democratic Party Chairman Rosalie Abrams, who squeezed Hughes' arm as he left the podium.

"Thanks, Rosie," the governor answered.

"You're making it tough on me," Senate Republican leader Ed Mason quipped, clapping an arm around Hughes' shoulders. "I'm supposed to say something nasty and here you come and give a good speech."

"I've been trying to make it tough on you for three years," Hughes muttered.

"I was very impressed. In fact I listened to the whole thing," said Sen. Thomas V. Mike Miller, a Prince George's County Democrat.

Hughes made his way down the House of Delegates aisle--he was stopped 36 times by well-wishers--and returned to his office for the usual lunch of beef bouillon, crackers and a Tab. He was jubilant, according to aides.

The 55-year-old governor decided about a week ago to deliver an unconventional speech, his aides said, because he felt his "message" was not reaching state politicians, who have often called him weak and ineffective. Elected in 1978 as a political outsider, Hughes has piqued many party regulars by eschewing the old patronage system and the bold leadership style of past Democratic governors. The speech, according to Goodman, was Hughes' way of explaining himself and his leadership style. "The governor just wanted to be the governor and he wanted to be himself," Goodman said.

But many in the audience insisted that they detected a "new Harry Hughes" today, and some criticized him for it.

"I was underwhelmed. I thought it was political theatrics," said conservative Democratic Sen. Francis X. Kelly of Baltimore County.

"No substance," huffed Republican Del. Constance Morella of Montgomery County.

In fiery tones, Hughes appealed to conservatives as well as liberals. He denounced a resurgence of religious and racial bigotry: "I want you to know that as governor, and as a human being, I am affronted" by it. And he also talked tough on crime: "If double-celling doesn't meet the courts' standards, well--double-releasing of hardened criminals doesn't meet ours."

Enthused and somewhat mystified by Hughes' surprise performance, legislators lingered for more than an hour to talk about the so-called new Hughes. "It was a new Harry Hughes, a super Harry Hughes," said Sen. Clarence Blount (D-Baltimore), a black caucus leader.

The comments appeared to irritate Hughes' press secretary and speechwriter, Lou Panos, a former Baltimore reporter credited with helping the governor recently to embolden his image. "This is the same Harry Hughes I knew back in 1954," Panos said.

"A new Harry Hughes? Nope," said Baltimore Sen. Harry J. McGuirk with a knowing wink. "Just a new speechwriter."