He has spent the last few days lining up financial support, ordering bumper stickers, searching for a campaign headquarters and finally coaxing longtime Democratic power broker Peter F. O'Malley out of political retirement. There is nothing official yet, but the meaning of all this is obvious.

Steny Hamilton Hoyer, former Maryland Senate president and golden boy of Prince George's County politics, is about to get into the race to fill the vacated congressional seat of Gladys Spellman.

As word spread yesterday that Hoyer was coming out of voter-imposed political exile, several other interested candidates said they would rethink their Congressional ambitions. Hoyer's critics, who for years opposed the tight control he and O'Malley exerted over the county Democratic party, began looking for candidates to defeat him or at least splinter the liberal and black vote Hoyer is counting on to win the upcoming special election.

Hoyer's decision to run for the 5th Congressional District seat ensures a tough Democratic primary between Spellman's husband Reuben, State Sen. Edward Conroy, possibly County Council member Sue V. Mills, as well as several others. Both Spellman and Conroy already have declared for the seat. Mills said yesterday that she is waiting until early next week to issue an official declaration.

Gov. Harry Hughes has not yet set a date for the special primary or for the general election, but he has said he would like the elections to occur as quickly as state election laws permit. In that event, April 7, the first available primary date, and a general election in mid-May are considered likely.

Hoyer's decision to enter the race became certain politicians asking for their support and some prospective opponents asking that they give their efforts instead to his bid to return to politics. Hoyer has been politically inactive since 1978, when he hopes for state office were dashed in an unsuccessful race for lieutenant governor.

Once the head of the Prince George's Democratic party, Hoyer has been hoping to return to politics but saw no immediate means for doing so until House Speaker Thomas P. (Tip) O'Neill's announcement last Friday that he would be vacating the Gladys Spellman's seat because of her continuing physical incapacitation.

Since then, Hoyer, like dozens of Democrats and Republicans around the county, has been attempting to gauge his chance of success in a potentially crowded special election. Hoyer apparently decided in the last day or so that he could obtain the support of most county Democratic officials and voters and persuaded O'Malley, who in the early 1970s organized the Democrats into a tightly controlled organization led by Hoyer, to emerge from retirment and run the special election campaign.

Hoyer's decision to seek the congressional seat drew a positive response from many of the Democrats who came up through the organization under his leadership and have complained since then that the party lacks organization. However, several of the so-called Independent Democrats, who ran in 1978 against the Democratic party slate put together by Hoyer and then-County Executive Winfield M. Kelley Jr., expressed no joy in hearing the news.

"We don't need him," said Del. Thomas Mooney, who ran against the slate and had considered running in the special election. "We want a candidate other than Hoyer for obvious reasons -- if he gets in he can move to put it back together and reunite the Democratic machine."

Mooney and several other independent Democrats have tried to persuade other candidates to enter the race in order to prevent Hoyer's election. Tuesday, a group of them appealed to Lt. Governor Sam Bogley to run for the seat but he turned them down. Earlier, one leader of the group, Del. Timothy Maloney, attempted to persuade Cora Rice, a black community activist in the county, to enter the race in order to pull off black votes that Hoyer could expect to win. She rejected the idea.