Las Vegas, Nev. — Last year it was merit pay. Now, the education theme that President Reagan is bringing home is classroom discipline. ''I can't say it too forcefully: To get learning back into our schools, we must get crime and violence out,'' Mr. Reagan told some 9,000 secondary-school administrators gathered here at a convention of the National Association of Secondary School Principals (NASSP).
''We must teach our sons and daughters a proper respect for academic standards, for codes of civilized behavior, and for knowledge itself,'' he continued, ''not for the sake of those standards, not for the sake of those codes, not even for the sake of that knowledge, but for the sake of those young human beings.''
The President also emphasized the importance of having high expectations for students, and he reiterated his ''back to basics'' theme. He also appeared pleased when his calls to restore prayer to the classroom received polite applause. Significantly, none of these items requires more federal involvement or federal spending. In an election year, that's important.
The issue of discipline was a major topic of discussion here, in part because many principals differ vehemently with comments by Reagan last month that characterized the nation's schools as dens of fear and disorder.
There has been widespread criticism that an administration report issued at the time of Reagan's comments relied on data from the late '70s, when many educators say discipline problems were much worse.
''President Reagan is wrong to emphasize the bad so much, as with the discipline question,'' said Curtis Drake, principal of the Brown Middle School in Hamilton County, Tenn. ''It is a problem, but there is also a need to emphasize the positive.''
Education Secretary Terrel Bell, speaking at a convention press conference earlier, appeared to tone down the administration stance on the gravity of the discipline problem.
''We want to emphasize that this problem is not nearly as serious - not of an emergency nature - as it was a few years ago,'' Secretary Bell said.
''We think the momentum to solve the problem was under way several years ago, '' he added. The administration's report, however, claimed that efforts to improve discipline were largely the result of the President's stand on the issue.
Nevertheless, Bell clearly captured the feeling of many principals when he said, ''For teachers, one of the most frustrating things is the disruptive student.''
He indicated that the administration is contemplating legislation to strengthen the hand of teachers and administrators in dealing with unruly students, but he said he was unable to give any specifics. The administration believes that court rulings in the mid-70s had ''gone too far,'' he said, in protecting student rights at the expense of general discipline.
The theme of the Las Vegas convention was ''Excellence: the principal's commitment,'' and the mood was upbeat and confident. The nation's principals are basking in the increased attention being paid education - and especially their role in improving it - in this election year.
While research in the late '60s emphasized the role of a student's home life in determining scholastic achievement, more recent studies have pinpointed the importance of a challenging and supportive school environment. And with the renewed emphasis on the school, principals have moved back in the spotlight.
Yet the principals appeared mindful of the fact that, to a large degree, schools have not regained the limelight for praiseworthy reasons. They realize that much of the increased attention is the result of reports and statistics revealing an education system that is not adequately preparing the nation's children for the demands of the coming decades.
According to Scott Thomson, executive director of the 33,000-member NASSP, many principals were initially quite defensive about the harsh criticism of the schools. ''We have worked to help them realize that this is the way the American public goes about improving things,'' Dr. Thomson said. ''It gets the dirty laundry out in the open - and then starts washing it.''
It was repeatedly noted that a successful principal is one who expresses leadership qualities, demands an orderly learning environment, holds high expectations for students, teachers, and themselves, and establishes a link with each student.
The corollary, however, was that principals, and even the schools, cannot reform education on their own.
''We know we need to change, but we also feel strongly that we can't do it alone,'' said George Piland, principal of J. W. Eater Junior High School in Rantoul, Ill. ''This is a big job, and it requires the cooperation of people outside the schools - the politicians, the parents, the businesses.''
Mr. Piland noted, for example, that legislators in his state are calling on schools to step up efforts to improve attendance. ''But in Illinois we don't even have a truancy law,'' he said.