One of the largest single-day exams in the history of American public education was given in Texas today, eliciting few complaints from the state's elementary and high school students. The youngsters got a holiday while 210,000 teachers and administrators, their jobs on the line, answered multiple-choice and essay questions measuring their competency in reading and writing.

It was the adult version of no-pass, no-play, but in this case it was no-pass, no-teach.

Educators who fail today's test, a major component of the state's education reform package, will have another chance in July. If they flunk it then, they are supposed to be fired. Texas Education Commissioner W.N. Kirby, who took the test this morning at Stephen F. Austin High School, estimated that 10 percent of the educators will fail the first time and that 95 percent ultimately will pass.

Although no boycotts were reported today, most teachers opposed the testing, saying it was embarrassing and unnecessary for certified professionals. Some teachers in Austin wore buttons that read: "Tests for Teachers, Polygraphs for Politicians." Others in Dallas entered the testing rooms wearing "Under Protest" stickers on their shirts. In Brownsville, a few teachers wore T-shirts that said "I Are a Teacher" on the front and "Me Not Scared" on the back.

The testing program in Texas is being watched by public educators nationwide. Ernest Boyer, former U.S. commissioner of education and director of the Carnegie Foundation for the Advancement of Teaching, has called the Texas test the "first big, serious, post-degree, post-certification look at the capacity, competency and ability of those who teach our children."

Two other states, Arkansas and Georgia, require experienced teachers to prove their competency through such tests, and more than a dozen states are considering similar legislation. Arkansas implemented its program in 1984, giving teachers three years -- and as many chances as they need -- to pass. Teachers who flunked the first Arkansas test will be weeded out only if they have not passed by 1987. Georgia exempts about half its teachers from testing. Texas exempts nobody, but, under emergency conditions, teachers will be allowed to work even if they flunk twice.

The impetus for competency tests has come mainly from southern states, where education reform movements have arisen after decades of minimal funding and academic neglect. To secure more money for the schools, and higher salaries for teachers, these states have sought to prove that educators were worthy of taxpayers' dollars.

"I think the tests will establish that Texas should be proud of its teachers," said Kirby, chief public educator in Texas, who noted that the test was not designed to gauge how good teachers are, but only whether they can read and write. "Then we can move on to creating a stronger climate for them. I'm really concerned about teacher morale. It's as low as I've ever seen it in 25 years. They think nobody likes them, that everybody's down on them."

Kirby, emerging from the Austin High testing room with a sweaty brow and a shirt pocket lined with No. 2 pencils, was asked whether he had trouble with the test.

"I didn't necessarily think it was that easy," he responded. Kirby said he studied for it by reading the review manual two or three times and watching a few segments of the TECAT (Texas Examination of Current Administrators and Teachers) Review on the local cable television's public schools channel. He said he thought the questions were on a 10th- to 12th-grade level.

Patti Turman, a fourth-grade teacher at Maplewood Elementary School in Austin, thought Kirby was being kind. "A piece of cake," said Turman, the first teacher to finish the test at Austin High. "A lot of my students could have answered those questions. If you flunk that test, you shouldn't be teaching. You shouldn't have gotten a certificate in the first place."