With parts of the country facing a bumper crop of disease-bearing ticks this summer and even more predicted next year, the government this week considers the first vaccine to protect against Lyme disease.

It's not a panacea: The vaccine won't prevent all Lyme disease, requires more than a year to build up immunity, and nobody yet knows how often people will need booster shots.But in regions where fear of Lyme disease is so great that many people head for a doctor as soon as they spot a tick, public anticipation is high as the Food and Drug Administration prepares to debate Tuesday whether SmithKline Beecham's LYMErix vaccine is safe and effective enough to sell.

"We're very excited about it," said Tom Forschner of the Lyme Disease Foundation.

Lyme disease struck about 16,000 people in 1996, the latest data available. Typically, it causes a telltale bull's-eye rash plus fatigue, chills, fevers and joint pain. Antibiotics can cure it - but if left untreated, Lyme disease can severely damage the heart and nervous system.

First recognized in Lyme, Conn., in 1975, Lyme disease is caused by a bacterium carried by pin-size ticks that live in wooded and grassy areas around the country, but especially in Northeast and North-central states.

A warm winter and lots of rain had health officials reporting an unusual increase in ticks early this spring, and experts already have environmental evidence that 1999 will bring an even larger population of ticks that carry Lyme and other serious diseases.

Doctors' advice: Use insecticide; check carefully for ticks; and when going into a tick-prone area like unmowed grass or brush, wear long sleeves and pants tucked into socks or boots.

But the tiny ticks are hard to spot and some patients don't suffer early Lyme symptoms, so not everyone at risk knows to seek help.

SmithKline's LYMErix, and a similar vaccine being developed by Pasteur Merieux Connaught, promise the first immune protection. The shots create antibodies that recognize an outer protein of the Lyme bacterium in a tick's saliva, called Osp-A, and neutralize it.

Unlike typical vaccines that work once an infection is inside the body, the Lyme vaccine essentially blocks the bacteria's transmission at skin level, explained Phillip Baker, a Lyme expert at the National Institutes of Health.

On Tuesday, SmithKline researchers will tell the FDA's scientific advisers that a study of almost 11,000 adults given either LYMErix or dummy shots showed the vaccine was about 80 percent effective.

There are caveats: It took three doses, the last given a full year after the first, to achieve maximum protection. SmithKline still is studying how often people will need booster shots. It worked better in people under 65. Studies in children, most at risk of Lyme because they spend more time at ground level, are just beginning.

And if the FDA ultimately approves LYMErix, that doesn't mean the vaccinated can get careless about ticks. It's not 100 percent effective and ticks carry more than Lyme.