When the head of the math department at Bethesda-Chevy Chase High School set out to hire an algebra teacher last March, she was shocked to find only eight names on a list of applicants provided by Montgomery County.

"Of those," said Patricia H. Tubbs, "some had already found jobs in county schools or had left the system altogether. Five years ago it would take only a day or two to find someone. This time it took over two weeks. But it could have been much, much worse."

Tubbs' story is not unique. At a time when applications for teaching jobs far outnumber openings, suburban secondary schools in the metropolitan area are facing a critically short supply of instructors in math, science and industrial arts.

Two years ago, for example, about 6,000 teachers applied for approximately 550 positions in Montgomery County. But only a handful of those sought jobs in math, science, special education, industrial arts and geography.

"There's a terrible myth going around that there's an oversupply of teachers," said Stephen M. Rohr, director of personnel for Montgomery County schools. "I have math applicants on file, but I don't want to hire people who don't come up to our standards. In science, math, special eduction and geography the shortage is critical."

Big-city school systems, where school discipline problems are more severe and salaries often lag behind those in suburban area, have experienced a chronic hiring pinch in those categories for years.

Mary Hendricks, a personnel administrator for the District of Columbia schools, said the District system never has been able to totally fill science, vocational eduction and industrial arts positions.

But, traditionally, the Virginia and Maryland suburbs, with their generally highly regarded school systems, attractive neighborhoods and competitive salaries, rarely had difficulty attracting highly qualified teachers.

But recruiters said the pool of qualified applicants has shrunk considerably in recent years. According to school administrators, the bulk of the applicants seek jobs in elementary schools in social studies or English, where there are no shortages.

But in math and science many applicants do not meet Prince George's, Montgomery's or Northern Virginia's comparatively high standards, creating a smaller and smaller pool from which to choose.

Other factors include the following: Teachers' salaries, which were closer to those of other professionals until the early 1970s, have not kept pace with other fields. In 1972, according to the National Education Association, a bachelor's degree in teaching fetched roughly $7,300 against $10,600 for a bachelor's in degree in engineering. By 1978 the gap had widened even more: Teachers could expect an average starting salary of $9,700; engineers at the same level could expect $15,600.

Math and science graduates are being increasingly into the private computer industry and government, where the demand for personnel has made the promise of career advancement brighter than in teaching.

Women and minorities, two groups which traditionally have filled classrooms, have found greater opportunities in other fields with the growth of affirmatives action programs.

College career counselors have steered students away from teaching. The number of students preparing for teaching careers dropped from an alltime high of almost 318,000 in 1967 to approximately 213,000 in 1977.

And teaching is simply becoming a less attractive profession as public pressures to cut education budgets grows and discipline in some schools deteriorates.

Witness Richard Zierdt, a 24-year-old long-term algebra substitute Tubbs was able to hire for Bethesda Chevy Chase.

Zierdt entered the profession "with a lot of excitement" three years ago, but has found limited rewards. "With kids today you sometimes get the feeling that they just don't want to be there (in school)," he said.

"It doesn't make your job a Whole lot of fun. Plus there's all the peripheral stuff you have to contend with, like students cutting class and setting up appointments to talk to parents about discipline matters. It's not really what the job is supposed to be about," he said.

Zierdt works about 120 days as a substitute teacher during the year, while he takes courses in computer math at Montgomery Colege. He plans to find work with a private computer firm.

Area school district have reacted by acclerating their national recruitment drives. A few years ago, with thousands of qualified applicants lining up to teach in Nothern Virginia, Faiefax County school officials had all but stopped active recruitment efforts.

But with a drop in applicants over the last four years, the school board this year budgeted $3,000 for recruiting and set out to find math and science teachers.

When John F. Schreck, personnel director for Fairfax County schools, showed up looking for math teachers recently at a Florida university, he found few candidates coming to his recruiting booth.

"So I eavesdropped on the booth next to me and heard industry after industry offer graduates $15,000 and up," Schreck said. "Our salaries start at $10,500."

In Prime George's County, George McCormick, superintendent of professional personnel, said his recruiters believe they are lucky if they see one or two science and math people on their trips to colleges. One result of the shortages, McCormick said, is a decline in the standards the county requires.

"qualifications are dictated by supply and demand," he said. "In science and math we've had to employ average applicants."

Similar stories are repeated in Prince William County and Alexandria. Even Arlington, which, despite a drop in enrollment from 27,000 to 17,000 students during the last nine years, is experiencing a shortage in special education teachers. For the first time in years the director of personnel for Arlington public schools has had to recruit actively.

If a report prepared by the Fairfax schools administrative staff is correct, the teacher shortage will become worse in years ahead. The report, based on national studies, predicts severe shortages in art, counseling, foreign languages, reading and business education.

It also notes that teaching is one of the most "depressing and unpromissing" professions. As Elton A. Bonner, a Fairfax school admininstator put it, "Teaching is not a funny thing anymore."