Charles County School Superintendent John H. Bloom said this week that improving the math skills of 604 ninth-grade students who failed a state test required for graduation will put "a staggering burden" on the system's teachers.

And it means the county will have to hire 20 to 25 additional elementary school teachers next fall to help prepare students, he said.

Bloom said he will ask the Charles County commissioners for an operational budget of $48 million to $50 million, including an additional $500,000 for teachers to reduce the average elementary class size of 27 to 24.

Bloom said his budget request, up from the current fiscal year's $43.8 million, "may give the commissioners anxiety pains" but is necessary if the county is to improve its statewide scores and cope with an overall jump in enrollment.

Of the 1,707 ninth graders who took the mathematics test in October, 1,103, or 64.6 percent, passed. Statewide, the 1984 passing average for math was 61 percent.

In Montgomery County, 79 percent of 7,776 freshmen passed the math exam, an improvement of 14 percent since the first tests were given in 1982. That year, only 65 percent of Montgomery's ninth graders passed, said James Meyerburg, head of the county's school testing office.

The recent test scores in Charles improved slightly over those of 1983, when 61 percent passed. But Bloom said the job of bringing more than 600 students up to state standards is placing a "staggering remedial load on high school staff."

The Maryland functional testing program was established three years ago by the State Board of Education to set minimal graduation requirements in reading, citizenship, writing and mathematics. This year's 10th graders will need to pass all four portions of the test to graduate in 1987.

With a per-pupil expenditure of $2,778, Charles County spends less than the other eight school districts in the Washington area to educate its students, county school spokesman Ashley Smith said.

Four teachers have already been added to the high school teaching roster to work exclusively with small groups of students who failed the math test, said Loretta C. Webb, an assistant superintendent.

But Bloom said it is unfair to lay the blame for math failures "solely at the feet of high school teachers."

"We will be concentrating our efforts at the middle and elementary grades because these ninth graders are tested six or eight weeks into the school year," he said.