The ballroom was festooned with helium balloons and old Hoyer for Governor signs recently amended to read Hoyer for Congress. Campaign stalwarts colloared politicians and gossiped about the upcoming special congressional election. And the band struck up 'Happy Days Are Here Again' as the candidate, Steny Hamilton Hoyer, waved out at the crowd.

"Isn't it great to see everybody back," sighed Winnie Kelly, the former Prince George's County Executive as he surveyed the scene, grinning at everyone who looked his way. Indeed, it seemed that everyone was back, the entire gang of pols, plotters and party loyalists who helped Kelly and Hoyer run one of the state's most powerful Democratic organizations until both lost elections in 1978.

There were the state senators and delegates, members of the County Council and 100 or more other Democratss who had come to hear Hoyer announce his candidacy for Gladys Spellman's seat, hoping the now fractured Democratic party would return to its former days of unity behind the golden boy why had been certain to carry Prince George's to statewide glory until he lost the Lt. Governor's race in 1978.

"We need Steny," said State Sen. Tommie Broadwater, one of Hoyer's closest allies, as he took the podium before Hoyer's speech. "He's gonna come back to Prince George's County and get the Democrats together and we need that."

Despite the show for strength for Hoyer yesterday, one which had been carefully planned for days, his ability to win the April 7 Democratic primary for the 5th Congressional District seat is far from the foregone conclusion it might have been several years ago.

For the party that he, Kelly, and Hoyer's close friend Peter F. O'Malley fashioned into a unified organization that some critics called a political machine has become a bunch of loose coalitions, frequently at odds with each other and distinctly uncontrolled. And, unlike the past, Hoyer's efforts to pull all his old friends behind him since Spellman's seat was declared vacant two weeks ago has not succeeded in eliminating some of the tough competition he will face in a primary race.

In fact, there are many politicians in Prince George's who believe that Hoyer is taking a risk running a race that for several reasons could leave him, despite his well-organized intelligence and political skills, a defeated candidate once again. Like County Council Member Sue V. Mills, who announced her candidacy Friday, Hoyer lives outside the 5th District, by only a few blocks, a fact that has already produced criticism by some opponents.

Hoyer hopes to overcome that obstacle by reminding people that he has countywide popularity, has lived for all but the last few years in the 5th District, and represented part of the district during his 12 years as a state senator. In addition, he says, when congressional redistricting is done next year, he is certain that the 5th District line will move south past his residence.

More of a problem in the upcoming special primary, is the field of strong Democrats that Hoyer is up against. Foremost is Spellman's husband, Reuben, who despite his age (71) and medical troubles (he had open heart surgery about a year ago) is the sentimental candidate of a large number of his popular wife's supporters. It is from this same group, liberal Democratic regulars, that Hoyer expects to go for support in a primary that could be won with less than 10,000 votes.

But Hoyer's advantage in all this is what allowed him to move up the political ladder from a precocious state senator to senate president to the gubernatorial heir apparent -- a well-plotted campaign. For the last ten days, he, longtime party strategists Peter O'Malley and Thomas Farrington and others have been callaing hundreds of party regulars, lining up support and developing a perceptible sense of momentum behind Hoyer.

They have collected several thousand dollars around the state, won the endorsement of labor groups, set up a Citizens for Hoyer and prepared to contact every Democratic voter who regularly votes in primaries.

While other candidates jumped into the race in some cases only hours after Spellman's seat was declared vacant because of her illness, Hoyer held back, floated his name as a possible candidate and waited to see what kind of support was out there. Instead of simply telling newspaper reporters he was running for the seat, Hoyer and his supporters spent several days planning yesterday's press conference and mini-rally to make the big announcement.

Finally, with all his old friends around, Hoyer made his quest official yesterday and, invoking the spirit of the Kennedys, brought up the issues he said would be a part of his campaign. Among other things, Hoyer said he would be a strong advocate for the county's numerous federal workers, support tax cuts that are not inflationary and push for a strong defense as well as nuclear disarmament. In addition, Hoyer said he would oppose any reduction in education aid or funds to the elderly and poor people and promised to resist what he called "the forces of single-issue and special-interest politics."