In most jobs, you're halfway between the 10 Year Club and a gold watch when you've worked 17 years. But Sharon W. Smith of Greenbelt and Thomas D. Cannon of Oxon Hill reached that landmark this year and got layoff notices.

Smith taught music, at Lyndon Hills Elementary in Capitol Heights, "because I wanted to teach kids to enjoy music as much as I did." Cannon, who taught at Potomac Senior High in Oxon Hill, decided almost two decades ago to specialize in driver education "because that was where the jobs were at the time."

They aren't there now. This spring, 20 driver education positions were eliminated in Prince George's County, and throughout the school system almost 550 teachers and other professional employes received layoff notices. In Baltimore City, 577 regular classroom teachers and about 200 teaching specialists were told they were no longer needed. School officials say at least 200 of these may be recalled. In Anne Arundel County, 58 teachers were handed pink slips, as were 47 teachers in Baltimore County.

The scene is being repeated throughout the state. Two years ago, more than 2,000 teachers were hired in the state. This year, the Maryland State Teachers' Association knows of only 100 vacant teaching jobs in six counties, according to association president Jancie A. Piccinini.

The number of vacancies will increase during the summer as resignations come in, and the MSTA is using a computer to try to find jobs for more than 1,000 out-of-work members. Most of the available teaching jobs are in math and science, Piccinini said, but few of the teachers laid off are qualified in these fields.

"There's almost nothing in the way of teaching except math and science," explained Baltimore City Teachers' Union president Irene Dandridge. So the union has taken a different tack: it set up two days of job interviews for teachers with representatives of corporations like C&P Telephone, Black and Decker and Baltimore Gas and Electric.

Smith, the Prince George's music instructor, met with hundreds of other county teachers at Largo Senior High two weeks ago to learn how to file for unemployment benefits. "Most of us are in my situation: We have never been on the dole in our lives," Smith said.

She filed applications for jobs in neighboring Howard and Montgomery counties, two of the most prosperous in Maryland. "They weren't very encouraging," she said. "But they said things may change."

Stephen M. Rohr, Montgomery schools personnel director, said the county has laid off four teachers and "we're not going to hire many." Few hirings are likely to take place before August, he said.

Last year, Montgomery hired about 300 teachers after the beginning of the school year. But this isn't necessarily good news, Rohr said, because many of the newly unemployed are "in fields where there aren't any jobs anyway. Physical education teachers, for instance, know perfectly well we don't have jobs over here."

They won't find jobs in Anne Arundel County, where 20 physical education teachers were laid off, or in Baltimore City, where 15 lost their jobs.

Howard County schools spokesman Paul F. Rhetts said an increased school budget has allowed 13 new professional positions, but he added, "I know of no vacancies at this moment, because of the number of people who are returning from educational leave or leaves of absence from the previous year. Those individuals must be placed first. In terms of actual vacancies, I'm not sure that there are any."

The situation may change later, he added. Many school officials say they expect resignations to come in later than normal. "Because the teaching market is tighter, people don't say they're leaving until they've got another job," said Joan Sorensen, spokeswoman for Frederick County Schools.

Enrollment in Frederick County is expected to increase next year from 23,459 to 23,532. "We're one of the few growing counties in the state," Sorensen said.

So far, she said, 20 full-time and nine half-time teaching positions are vacant. These include vacancies for elementary school teachers, kindergarten teachers, art and music teachers, vocational education teachers, science teachers, a language arts teacher, a social science teacher and special education teachers. There also are openings for two language instructors, Sorensen said, because of a reviving interest in Latin.

Teaching jobs will be found south of Prince George's only by sheer luck. Charles County is losing 20 positions next year and Calvert County is losing six. There are no new jobs in St. Mary's County. "We can find all the people we need, with the exception of math--that's the premium," said St. Mary's schools spokeswoman Dolores T. Fleming.

Richard L. Holler, spokesman for Calvert County schools, which will employ 462 teachers next year, said there may be vacancies "in the areas most difficult to fill, such as higher maths." No higher math teachers were laid off in Baltimore City or Prince George's.

Despite the large number of teachers losing their jobs this year, Maryland school districts reported they are receiving few applications. One of the reasons is that people like Cannon, the driver education instructor, knows his skills aren't needed by school systems that do have vacancies and is trying to "re-tool." He hopes to become qualified this summer to teach social studies and to find another job with Prince George's schools.

Another reason for the decline in applications is that fewer people are graduating with teaching degrees. Montgomery personnel director Rohr says applications are down because recent college graduates going into education are looking for work in Sunbelt states, where more jobs are available.

According to the National Education Association, the number of instructional staff in the nation's schools, after increasing through most of the past decade, fell by 0.5 percent last year. But in Maryland, the number fell by 3.6 percent as enrollment dropped by 3.8 percent.

In contrast, the instructional corps in Texas public schools grew 2.8 percent last year, adding almost 4,500 classroom teaching positions.

Enrollment at the University of Maryland's College of Education in College Park, the largest teacher-training school in the state, has fallen drastically since 1971. Ten years ago, the undergraduate enrollment was 5,217; this year it was 1,660. The number of graduate students has fallen from 2,210 to 1,748.

Students considering professional careers "respond to the demands in those professions," explained George Marx, acting director of the the university's College of Education. But he predicted more teaching jobs will become available in Maryland by 1986 or 1987. Currently, he added, "there's a shortage in math and science, in industrial arts, special education and English. A person beginning college now can predict there would be job opportunities" by the time he or she graduates.

Marx attributed the improvement to a "baby boomlet" expected to affect elementary schools about that time. But most union and school officials blame teachers' employment problems on tight budgets rather than declining enrollment. "The cause of all of it is budget cuts," said MTSA president Piccinini.

University of Maryland professor and school financing expert Eugene McLoone said federal cuts and inflation, a lower level of public interest caused by lower enrollment, and a period of recession have had a cummulative effect on school funding. These problems are accentuated in Prince George's by property tax limitations, he said.

"By and large, wherever there are restrictions on property tax, education in elementary and secondary schools is hurt the most," McLoone said. "I have no explanation for that, but it has been a universal kind of thing. Education drops much more than other services.

"The other thing that seems to be fairly clear is that fighting crime is much more important to people right now. So you have two kinds of situations working together."

Things are less clear to people like Scott, however. "I've been doing my job for 17 years, and I do it damned well," she said. "And all of a sudden I've been cut off. Why? This is really devastating."