Steny Hoyer, the former Maryland Senate president who dominated Prince George's County politics until his defeat in 1978, has been asked by the county's top Domocratic officials to fill a vacant seat on the county council.

The draft-Hoyer movement emerged unexpectedly this weekend after the local party's Democratic officeholders gathered privately to agree on a replacement for Francis B. Francois, whose retirement leaves a vacant council seat that must be filled by Oct. 5.

Hoyer had not put his name forward during the past weeks of public hearings and Democratic party central committee meetings that had been called to come up with a successor to Francois.

But in the last few days, as six candidates for the council seat emerged, it became apparent to many members of the party that the selection process had not produced a candidate on whom all factions of the splintered party could agree.

In this context -- amid growing awareness that the once well-organized and powerful party had slipped into disarray form which it might not recover by the next election in 1982 -- Hoyer's name emerged at a meeting of State senators early Friday morning.

Hoyer said he was surprised to learn that his long-time friend, State Sen. John J. Garrity, had brought his name up at the meeting as the candidate the influential group should support.

Hoyer said he had been approached weeks ago by several party leaders to apply for the seat, but had declined to do so because he was not interested in leaving private life and his successful law practice.

The senators' new request, however, prompted Hoyer to reconsider. He said he would decide by Monday whether to actively pursue the post, which, because of his earlier accomplishments in the party, would be guaranteed him if he wanted it.

If he were to take the position, Hoyer said, it would be in a "caretaker" role, solely to finish out the remaining two-year term of the council. After that, it is widely expected that he would run again for statewide office -- possibly governor or senator. Hoyer has been out of office since 1978, when he ran and lost as a lieutenant governor candidate.

A Hoyer decision to go for the council seat would have a profound impact on the county Democratic party and on the process that has been underway since July to find a replacement for Francois.

Most important to party officials, it would being some cohesion to the party. Since Hoyer's defeat and that of former county executive Winfield M. Kelly Jr. the party has been without any clear leader, leaving it powerless in Annapolis and unable to counteract the current Republican county executive.

Although a council position is considered less powerful than the state senate post Hoyer previously held, his past dominance of the party and the ties of loyalty would assure him a leadership role.

Said one county politician: "His coming back in would fill the top rung of the [political] ladder. There's no one there now who can pull the party together. Steny's coming back it would firm things up very quickly. Considering '82, we have a very short time to get this party together."

Hoyer's decision to reenter politics at the county council level also would add a strong possible contender for county executive in 1982. The Democrats have spent much of the last year worrying that they will not be able to field a strong challenge to the incumbent Republican Executive Lawrence Hogan.

In a more immediate sense, Hoyer's decision to go for the council post would disrupt the selection process that has been underway for several weeks and within the last few days had entered its final stretch.

Unlike past years, when Hoyer, Kelly and other party leaders held regular breakfast meetings to select candidates and make appointments, such decisions now are made by the 24-member Democratic Central Committee.

After holding two public hearings this summer to consider 22 applicants, the committee came up with a list of six names, which did not include Hoyer. Various factions of the party were to meet Tuesday morning to cut this list to three of four names, which then would be sent to the central committee for a final vote.

In September, the council was to make the final selection of Francois's successor.