The Prince George's County Council tentatively agreed yesterday to add $5 million to the $300 million recommended by County Executive Lawrence J. Hogan for the operation of the county's school system next year. The action still left the budget $31 million short of the $336 million sought by the school board--and $3 million less than the schools had this year.

The council approved a series of minor cuts in several other departments and a number of accounting changes to give the school board something more than Hogan proposed in his March 31 budget message.

Despite yesterday's additions, according to school board and council staff analyses, the schools face the prospect of either reopening a negotiated contract or laying off between 200 and 1,500 employes. Council members said that despite their efforts to assure a level of funding at least equal to this year's, the money was not available without serious disruptions to other departments.

Though yesterday's actions were taken in a work session and are not final, the council has only a week to approve its final budget, and school officials said they were resigned to the consequences.

"What I will have before me is 15 days to notify employes that they're not going to have a job," said Superintendent Edward J. Feeney. He said he expects the schools will have to lay off "very close to 1,000."

Hogan, who has maintained throughout the budget negotiations that massive layoffs will not occur, said through a spokesman that he continued to believe that layoffs can be avoided.

Council Chairman Gerard McDonough yesterday blamed the county's charter-mandated tax limitations (TRIM) for causing the fiscal constraints, but said that even without the law, reductions in the school system were likely.