Prince George's County School Superintendent John A. Murphy wants $475.9 million for the 1988-89 school year, a 10.5 percent increase over current spending, his office announced yesterday. Characterized by officials as "conservative and prudent," the spending request was still higher than the school spending limit suggested by County Executive Parris Glendening.

The area's second largest school district also disclosed plans to expand the county's desegregation efforts with 11 new magnet programs next fall, including communication arts elementary schools and career high schools with special programs in banking, finance and biotechnology.

The future of the magnet program, now in its third year, has been a key issue as officials continue to coordinate 39 programs while juggling the racial balance among its 171 schools.

Under Murphy's recommendation, unsuccessful extended-day programs in two elementary schools would be replaced with the communication arts programs, which emphasize writing and language skills. New middle and senior high school programs were proposed to accommodate the growing numbers of pupils already in elementary school magnet programs, particularly mathematics and "traditional academy" programs.

The popular college preparatory "University High" program, now used to attract white students to Suitland High, would be duplicated at Laurel High School where admissions guidelines would favor black students.

The new magnet programs would not pose a significant extra strain on the budget, officials said, adding just $1.2 million to the $23 million earmarked next year for the desegregation plan. The county hopes to get as much as $11 million in state funds for the program and another $4 million in federal funds.

The proposed budget contains few of the instructional improvements -- smaller class sizes, bus service for more primary pupils, more computer equipment -- that school officials have long insisted are necessary to improve education in the county's nonmagnet, neighborhood schools.

"It's basically a hold-even budget," school spokesman Brian J. Porter said yesterday.

Last year, the County Council cut the school spending plan by $15 million, shaving off most of those improvements. Then, government officials and educators were at times publicly at odds over educational spending, which this year accounts for 57 percent of the county's budget.

School officials said they were being less expansive in this year's spending request.

"It is because we knew there was only but so much money to be had," Board of Education President Barbara Martin said, recalling budget discussions last month with County Executive Glendening. "Even as conservative as it is, we're still not sure about the funding."

In a written statement released yesterday, Glendening called the school budget reasonable but repeated that he wants to limit the increase to $25 million.

Murphy was unavailable for comment on his budget proposal yesterday. The increase falls in line with superintendents' spending proposals at the area's other major school systems. Fairfax County is asking for a 9 percent increase, while Montgomery County has sought a 10.6 percent rise. Although D.C. School Superintendent Floretta D. McKenzie sought a 6 percent spending increase, the school board said it wants 12 percent.

The Prince George's proposals for fiscal 1989 includes an additional $1.3 million for new text, library and reference books, updated maps and globes and other supplies, a request that was denied last year.

More than $30 million of the $45.1 million budget increase would pay for increases in employee benefits -- such as a 25 percent increase in health insurance premium rates -- and the previously negotiated 7 percent pay raise for teachers and 6.1 percent for other employees. The raises are the last in a three-year contract and would boost starting teacher pay to $21,591.

School officials also said more money will be needed as enrollment continues an upswing. Enrollment is expected to climb next year by 1,374, to 104,699 students, requiring the hiring of 164 more teachers. The spending proposals would increase the amount that the county spends to educate each child by $361, to $4,516.

A program for potential dropouts and other high-risk students is among the new priorities in the school budget. Officials want $2.8 million to expand Project Success to all senior high schools. The program, now at six of the 20 senior highs, has been credited with improving attendance, grades and behavior of students who have had difficulty learning and adjusting to the regular classroom. It is viewed as an important tool in addressing behavioral problems as measured by the county's high, and controversial, rate of student suspensions.

Public hearings on the proposed school budget will be held Jan. 20, 25 and 27, and the Board of Education is expected to submit its final request to the county executive by March 1. Hearings on the new magnet programs will be held Tuesday and Jan. 21.

Under the superintendent's recommendations, Largo High School would open next year with career programs in banking, finance and entrepreneurship. They and a biotechnology career program planned at Fairmont Heights High School are designed for both college- and noncollege-bound students and are separate from traditional vocational studies. The programs are proposed to attract more students to these increasingly predominantly black schools.