Sometime within the next few weeks, according to an unwritten but established schedule, John J. Carrity will get the nod. There are many others who want it, but Garrity is supposed to get it. The nod is not something that the Democratic Party leadership in Prince George's County leaves to chance.

In most cases, getting the nod means that a political candidate has been chosen to run in a primary election on the ticket created by the Party organization. For Garrity, a member of the Maryland House of Delegates, it means that he is expected to be chosed to serve out the term of state Sen. Meyer M. Emanuel Jr., who is resigning from his Hyattsville-area seat effective Jan. 8.

The process is generally the same. It involves hearings, resumes and interviews. There are deliberations by committees. There is praise for the openness with which matters are handled, and there is, from beginning to end, very little doubt about who is getting the nod and who is giving it.

The jump from delegate to state senator is an important one for a politician. A senator gets more power, more perks and more press and is taken seriously. It is moving into the big leagues.

It is 7:30 on a Monday night. There are about 80 people filling the wooden benches of a second-floor courtroom at the County Service Building in Hyattsville. The crowd is said to be the largest of the year for this performance by the Democratic Central Committee , which for the first time in recent memory, has a state Senate seat to hand out.

"We're here to carry the fight for Joey," says a deep-voiced, elderly woman who wears a gray pinstripe suit and has closely cropped gray hair. "Its gonna a be a tough one but we're here to try it."

The woman is Rose Sullivan "Joey" is her son, Charles Joseph Sullivan Jr., delegate from Prince George's County's 22d district, applicant for Emanuel's Senate seat. The "we" is five elderly women wearing "senior power" buttons.

"Joey" has the large-boned appearance of his mother. Her voice is firm, his is hesitant. She looks at the situation in terms of power. So does he.

"I think I have an excellent chance of getting the nod," he says. "I led the ticket in the 1974 primary and the general election. I got more votes than Emanuel and Garrity both times. I have support throughout the district.

"I've called the leaders and told them I was seeking support. I called (Maryland Senate president and gubernatorial candidate Steny Hoyer and (County Executive) Winfield Kelly. They thanked me for calling. I've always been a supporter of Kelly myself."

In the courtroom with Sullivan on this night are a few assistants to Kelly and Hoyer. They are adept at political translations. Sullivan, they explain, has really said: "If I don't get the nod, I will run against Garrity in 1978."

These assistants are also adept at spreading the word for their bosses. They do it quietly, calmly, rarely for attribution, without frantic telephone calls, without pressure.In the friendliest of tones, they question Sullivan's abilities and his politics.

Ann Hull, a Takoma Park resident, is the House delegate from the 22d district. She has served in Annapolis since 1967, the last session in a leadership position as speaker pro to tempore. She, too, has applied to the central committee to be considered as Emanuel's successor.

There was a time when Hull who has worked for Central Intelligence Agency and the League of Women Voters, had reason to believe that she would get the nod. Garrity, like most lawyers, always wanted to be a judge. He was in the running for a District Court judgeship in Prince George's this year as a possible replacement for Vincent Femia, who recently moved up to appellate level.

There had been an understanding until this Monday night that Garrity would rather be a judge than a senator, and that if Acting Gov. Blair Lee Ill appointed him to replace Femia, Ann Hull would get the Senate nod. She would then become Prince George's first woman senator.

But Garrity is the first speaker at the central committee meeting, and he says right away that despite his "strong personal preference" for the judgeship, he has decided that it would be "in the best interests of his constituents and the party" if he took the nod for the Senate.

Hull offers the translation this time "It means he has it," she explains. "It means he had weighed what is certain and what is not certain." Hull has talked with Hoyer and Kelly and she "has not been particularly encouraged." But she will go through with the process, she will not withdraw."

"Nothing is certain in politics," Hull says, "until it has actually taken place."

Claire Bigelow, another applicants, disagrees. She looks at politics as a series of certainties, one being that she will not get the nod, another being that Garrity will get it.

"There is some question as to whether one should even take part in a charade of this sort," says Bigelow of the selection process. "It is always decided beforehand."

Bigelow, a leader of the Maryland Women's Political Caucus, is no friend of Hoyer or Kelly. Hoyer didn't particularly like the fact that in 1976, when Bigelow was a delegate for presidential candidate Jimmy Carter, she refused to vote for Hoyer as an at-large member of the delegation. Kelly refused to reappoint her to the county's Commission on Women after several run-ins with her last year.

"They know that I'm going to run for the Senate seat next year if Garrity gets it," says Bigelow. "There is no other choice. They've already made it clear that there won't be room for new people next year. They'e closing the circle around the people already in it."

Jeanne M. O'Neill is a member of the Prince George's County Democratic Committee. She is one of 11 members who will officially decide who will get the nod.

"I'm surprised," says O'Neil hours before the hearing. "I haven't heard from anyone about this. Usually, I get letters or telephone calls from this person or that person. I would expect that kind of thing for something as important as a Senate nomination, but it hasn't happened."

O'Neill is one of six committee members who show up for the hearing. Only three of those six were elected in the primary of 1974, the other three, including O'Neill, Charlotte Johnson and John Foran, were appointed by the party leadership following resignations.

The hearing is chaired by Lance Billingsley, official chairman of the county party, law partner of William Meyers, who is to Winfield Kelly what Peter O'Malley, one of th county's dominant power's is to Steny Hoyer. When word first got out that Emanuel was resigning, billingsley expressed some interest in the job himself.

His interest did not last long. It was suggested to Billingsley that it would not look good if he went up against the three delegates from the district. This was not the right time for him to enter elective politics. Thus came his comment:

"I had to consider the effect on my family and my law practice. If I went to the Senate, we would have to disolve the practice, because we appear extensively before administrative agencies. I started the law firm two years ago and have built it up I want to build it some more before I seek political office."

As chairman of the county Democratic Central Committee, Billingsley is also the moderator of the Democratic Advisory Committee, known more commonly as the "Breakfast Club." This club - composed of the eight senators, four of the 24 delegates, the county executive and a few others - does not advise the central committee so much as it does the work of the central committee.

The nod is given by this club, which will meet Monday morning to discuss th Senate seat. Then, as Billingsley explains: "The central committee deliberations are done in executive session. What we try to do is reach a consensus decision. There is nothing, however, to peclude a vote being taken."

Jack Garrity sits alone in the back row of the courtroom. He has already made his contacts. He has talked with Peter O'Malley, an old law and tennis pal. O'Malley told him: "Jack, I'm for you whatever you decide."

He has talkd with Steny Hoyer, ranking member of the county legislative delegation. Hoyer told him he would rather have Garrity running for the Senate on the ticket next year than sitting up on the bench. But again, it is up to Jack.

Garrity has talked with Winfield Kelly, a power to be dealt with apart from O'Malley and Hoyer. Kelly has told him he wants Garrity in the Senate. "Jack is tough, he's a bulldog," explains a Kelly assistant.

"You give him the right program and he'll go with it. And he's loyal. you can set him out there in the 22d district and know that there will be a dependability about him. That's what Kelly is looking for in the senators now. He wants the eight senators to set up their own freedoms, to take the hat off the people up at the top."

So dependable Jack Garrity, with his soft voice and sandy gray hair, sits in the back row and talks confidently about getting the nod.

"You know," he says, "I have acted in the role of being the cement that binds the Hoyer-O'Malley faction with the Kelly faction. I go way back with Pete (O'Malley), and I made my political alliance with Kelly back when we were both on the County Council. We were in different factions, but we joined together to oust the Spellman faction led by former council member and current U.S. Rep. Gladys Spellman from Council control."

Garrity notes that he considers O'Malley, Hoyer and Kelly to be among his best friends. "It is to their benefit and to to the benefit of the constituents of the 22d," he says, "that I be in the Senate rather than on the bench."