Prince George's County school principals and supervisors notified 827 teachers and other employes yesterday that they will no longer be employed as of July 1.

The reduction-in-force notices were delivered instead of being mailed today, as previously planned, because Superintendent Edward J. Feeney wanted to speed up the procedure.

School spokesman Brian J. Porter said school officials wanted the riffed employes to get notification from "an immediate supervisor, someone they knew," rather than "receive a nondescript letter in the mail."

Meanwhile, the leadership of a union representing 3,500 bus drivers, custodians, clerical and instructional workers will advocate a package of contract givebacks to their membership at a meeting tonight. Jim Shearer, head of AFSCME Local 2250, said the concessions could save the jobs of all 150 AFSCME members who received notices yesterday, as well as 110 members who will be demoted as a result of the budget cuts.

"We don't like the word concessions," Shearer said. He said he preferred terming the proposal "alternatives to layoffs."

Leaders of the teachers union, whose members received 434 layoff notices yesterday, voted overwhelmingly Monday not to give up contract benefits to save jobs. But Shearer said that the decision should have been made by the rank and file.

"The overwhelming calls coming into this office were in favor of doing something to avert the layoffs," Shearer explained. "We feel we have a responsibility not only to the people who didn't get riffed, but to those who did," Shearer said. "We feel that our members ought to make that decision--it shouldn't be decided by the leadership who in most cases are senior people not affected by the rifs."

For the riffed teachers, yesterday's notification came as a shock despite a week of publicity.

"Some of them didn't even know they were being considered," said Diana McCusker, a biology teacher at Oxon Hill High School and president of the County Council of PTAs. "I have never seen such a quiet faculty room. What do you say to somebody who you thought you were going to be working with and now they don't have a job?," McCusker asked.

The principals received their respective lists Tuesday afternoon and were instructed to withhold the names until yesterday. But when Mary-Dean Floyd saw R. Dean Powell, principal of University Park Elementary School, at a PTA meeting Tuesday night, "all I had to do was to look in his eyes and I could tell," said Floyd, who was one of 55 elementary librarians laid off yesterday.

"The first thing this morning the two of us just stood there and cried over the whole thing," said Floyd, who ran the school's large and innovative media center for five years.

"It's the center of our building, both architecturally and instructionally," said Powell. "Anyone else I'll get will just be a name coming across a desk to me."

The layoffs at University Park are typical of elementary schools. Powell said the school's full-time librarian and reading specialists will be changed and reduced to half time, and the school will lose one classroom teacher as well. The school PTA plans to rally in front of the county administration building today to protest the budget cuts--part of what county PTA head McCusker called a growing grass-roots reaction against the austere county budget.

Several PTAs and at least one student group are planning to join the teachers in a "march on Upper Marlboro" next Monday.

At the urging of the County Board of Education, each of the system's 116,000 students were going to be asked today to write letters to President Ronald Reagan and to Congress, but the Maryland attorney general's office advised school authorities against the demonstration.

The letters were to remind the leaders of the value of education in the face of declining federal support for schools.

School spokesman Porter said the ruling "has something to do with involving students with political endeavors. As such, it was outside the legality of the school system and it was canceled."