WHILE most members of the Sanford (Maine) High School marching band were playing music at a state band competition earlier this winter, nine members were secretly tripping on LSD.
School officials eventually suspended the band members. But state officials saw the incident as a wake-up call. ''What we are seeing in Maine,'' says Sgt. George Connick, a supervisor at the Maine Drug Enforcement Agency, ''is a moderate increase in the use of LSD among young people.''
In this case, as Maine goes, so goes the nation. Use of LSD, the illicit hallucinatory drug synonymous with the 1960s, is now reported to be slowing rising among youths in national and state drug surveys and reports.
The United States Drug Enforcement Agency (DEA) goes further. It calls LSD (lysergic acid diethylamide) ''the fastest growing drug of abuse among the under-20 age group.''
A recent report by the National Institute on Drug Abuse (NIDA) surveyed 50,000 secondary students in the US. Marijuana was identified as the drug experiencing the ''sharpest increase,'' but the report concluded that ''LSD [and] hallucinogens other than LSD ... also continued to drift upward.''
In 1991, 2.7 percent of eighth- graders had used LSD. Last year, that figure rose to 4.4 percent. The proportion of eighth-graders taking any illicit drug has grown since 1991 from 11 percent to 21 percent.
Almost all experts agree today that LSD, inhalants, marijuana, cigarettes, and alcohol are being used by more and more children at younger ages. All drug use is up among kids in junior high and below, and it has edged up again in the past three years among 12th-graders.
The NIDA study, conducted by the University of Michigan annually for the last 21 years, indicated that the proportion of all students regarding drugs as dangerous continued to decline in 1995. Other studies indicate that LSD is often perceived more as an exciting stimulant than as a drug with potential harm.
Yet there were reports last year of deaths and violent behavior of teens related to LSD use. Recently, a 16-year-old in Barnstable, Mass., died after ''acute psychosis'' induced by LSD, according to a medical examiner.
What particularly bothers observers now is the increasing frequency of LSD use.
''The disturbing factor is that LSD is taken now on a much more frequent basis by those who use it,'' says Jim Hall, executive director of Up Front Information Center, a drug research center in Miami, Fla. ''With a lower dose level, we hear of far more regular use, even daily use by some students.''
Social scientists say that the national increase in the use of LSD stems from several causes. First, the drug is relatively cheap. A small dose of LSD can be bought for as low as $3. Second, a decade ago there was more attention in the media about the consequences of drug abuse, and more antidrug ads. Third, many teens are not informed by parents about drugs.
According to the University of Michigan report: ''Parents of a decade ago may have been more likely than today's parents to talk to their children about drugs, because more of today's parents actually used drugs when they were teens and may feel hypocritical telling their teens not to use (them).''
The LSD of today generally tends to be less potent than the ''acid'' used in the 1960s and '70s. While the drug is not considered to be physically addictive, like cocaine or heroin, it can become a drug of dependency for some users.
''This is not a drug that is usually identified with dramatic, emergency-room conditions with an overdose, although it does occur,'' Mr. Hall says.
''In fact,'' he adds, ''there is a lot we don't know about regular daily use of LSD. What will be the effect on a person who is 15, and then when they reach 30? Among young groups, there is an attitude that it is not as harmful as cocaine or crack. They say, 'I don't do drugs. I just drop acid.' ''
While information is still lacking about the full impact of regular LSD use, the effects of one dose of LSD can last as long as eight hours. When a ''bad'' trip occurs, the tendency for the user is to think he or she had a ''bad'' dose.
''It's like being in a wild movie,'' says Mr. Woolley. ''The kids think they are thinking these great thoughts, getting a new awareness of themselves. They think it sheds new light on their situation.
''But it doesn't,'' he adds, ''because once it's over, it's back to reality. The more they use it, the more they become alienated from society.''
Some drug experts say that LSD's sporadic availability in communities - linked to the fly-by-night nature of LSD production - causes the drug to be evident in spurts. ''It certainly is not used at the levels it was back in the 1970s,'' says Leigh Henderson, a drug researcher and co-author of the book, ''LSD: Still With Us After All These Years.''
Officials say that because the drug is difficult to make, sophisticated knowledge of chemistry and labs is required.
Clandestine laboratories at universities are sometimes the source of the drug, says Ron Woolley, a street worker for The Bridge, a youth organization in Boston.
And according to the DEA, makeshift labs in the Northwest, particularly in northern California, also make LSD fairly quickly in concentrated amounts. Then the labs disappear to avoid apprehension. The labs make thousands of doses, usually tiny specks soaked into small pieces of blotter paper. The pieces are sold as ''hits,'' to be swallowed or chewed.
''There are sophisticated marketing schemes used,'' Hall says. ''An individual can order through the mail from a known contact. It comes in an odorless letter, hundreds of doses on several sheets of paper.''
Hall and other experts also cite rock-band tours as sources of LSD distribution. ''People who are touring with [these bands] come into town and distribute to their friends,'' says Mrs. Henderson.
Inner-city teens are not known to be users of LSD. The most use comes from white, middle-class teens in the suburbs.
''What concerns me is that it is usually not the first drug a youth has used, or the only drug they will be using. It is an indicator of probable use of other drugs by an individual,'' says Henderson.
Because attitudes shape behavior, experts say that schools, parents, the media, and law-enforcement agencies need to take a renewed and vigorous stance against illicit drugs.
''This is not a runaway epidemic among teens, but it gives rise to caution,'' says Lloyd Johnson, a University of Michigan social scientist and the lead researcher on the NIDA study. ''Our great progress in the past at lowering rates of illicit drug use among our young people is proof of that.''
Between 1979 and 1992, with a concerted government and community antidrug effort on a national basis, the proportion of 12th-graders reporting use of drugs fell from 54 percent to 27 percent. Since then, use among 12th-graders has edged upward.
The penalty for possession of even a few grams of LSD today is a minimum mandatory federal sentence of 10 years.