Public school is supposed to be free. But a student at Walter Johnson High School in Bethesda can expect to pay $15 to take Advanced Placement biology, $40 for band class and $11 for a Spanish workbook.

Lab fees, band fees, art fees and ill-defined "activity" fees are proliferating in cash-strapped public schools at a time when many families are watching their spending. This month, some Montgomery County parents mounted a campaign to challenge such fees in a dispute that might land in court.

Virginia has begun an effort to standardize rules for fees that vary from school to school. Last spring, an advocacy group for the poor reported that a Virginia mother of three borrowed against her car title to come up with $260 in school fees.

"Each school's fees are just whatever they feel like they can charge," said Louis Wilen, a Montgomery parent who is a leader in the fee debate. "The law says that schools are supposed to be free."

However, schools routinely charge students for goods and services and contend that the fees are permitted by state law. There are often fees for items such as workbooks, computer supplies, paintbrushes and gym suits. In addition, schools sometimes charge for use of lockers, musical instruments, football uniforms and parking spaces. Students who owe money may be excluded from graduation or be denied a report card.

Without fees, education officials say, schools might have to cut courses, swap acrylic paints for pencil and paper or send the band onto the field in T-shirts.

"The reality is that the money has to come from somewhere," said Brian Edwards, chief of staff to Montgomery schools Superintendent Jerry D. Weast.

While Montgomery schools have drawn much of the backlash, fees are everywhere. The kind and amount vary by school and county.

Loudoun County charges for student parking and gym uniforms but not for art supplies, computer disks, workbooks, science lab materials or towels.

Calvert County allows high schools to charge 12 curricular fees. Among them: $20 for gym uniforms; $45 for shoes in the Dance for Athletes class; and a $20 lab fee in graphic arts. Most workbooks and lab materials are provided without charge.

Fairfax County allows schools to charge for musical instruments, parking, performing arts materials, towels and uniforms in occupational classes, but not for workbooks, traditional science labs or art classes.

Montgomery does not bar schools from charging any specific fee but guarantees that students will receive "content material required to meet course outcomes" and that they will not be penalized academically for inability to pay.

The list of approved fees for Montgomery schools runs to 48 pages. Many of the charges are presented to parents as "course fees," with no hint of their purpose.

Col. Zadok Magruder High School in Rockville lists 24 fees this school year covering at least twice that many courses, ranging from $5 to $40, according to a school document parent activists obtained. Walter Johnson charges 49 course fees, ranging from $4 to $40. Thomas Edison High School of Technology charges as much as $400 for a class in cosmetology.

Beth Kaufman of Bethesda spent about $107 last year to supply her twins, then eighth-graders at Takoma Park Middle School: $10 for assignment books, $8 for lockers, $24 for Spanish workbooks, $5 for orchestra class and $60 in extracurricular activity fees.

She said that this year, at Montgomery Blair High School in Silver Spring, , "my kids have been asked for exactly zero dollars so far. I don't know if it's because of all the parent agitation."

Opposition to fees in Montgomery emanates from a watchdog group known as the Parents Coalition. Its leaders urged parents to oppose the fees at the classroom door. School officials responded with an Aug. 19 memo to principals, clarifying that it was all right to charge fees but not to penalize students who do not pay.

The fee debate has raised legal questions. In 1987, the Maryland attorney general interpreted the state's guarantee of free public schools to mean "that everything directly related to a school's curriculum must be available to all free of charge." That opinion is key, as no state court has ruled on the legality of fees in the modern era.

Montgomery officials have suggested that schools are merely asking parents to pay the fees, and that all required materials will be provided. But schools seldom characterize fees as optional, in Montgomery or anyplace else.

"The families are led to believe that the fees are mandatory and that the students won't be able to get their schedules and participate in activities and graduation if they don't pay them," said Angela Ciolfi, an attorney with the Legal Aid Justice Center in Charlottesville.

Ciolfi's group used public records requests to determine that many Virginia schools had no formal policies on fees. The findings prompted the state education department last spring to survey school systems. Of 83 systems that responded, 64 said they charged fees. Most of the 64 said they had a policy on fees. Fewer than half said they had rules for what to do when a family seeks financial help.

Virginia law on fees is more explicit than Maryland's. It allows schools to charge students for workbooks and for transportation to extracurricular activities. It does not allow schools to withhold report cards and diplomas from students who fail to pay. State regulations are being rewritten and will provide further guidance, Ciolfi said.

Montgomery's school board will meet in a closed session Sept. 9 for legal advice on fees, and administrators are studying the policy. Board members have little to say publicly on the matter.

"Do I have a doubt that some of those fees on the 40 pages of fees are on the other side of our policy?" said one board member, who requested anonymity to discuss the matter candidly. "I have no doubt in my mind."