Sumer is acumin in and loudly sing . . . It's not just Chaucer's immortal cuckoo singing, but everybody else as well. It's playtime.

But there's a catch to everything. (Even Madame Cuckoo, herself, has a disposition that's hardly worth immortalizing. She's the bird who lays her eggs in another bird's nest and then flits off to sing in some poet's ear . . . leaving her baby cuckoos to tak over, pushing their step-siblings right out of the nest.)

Summer is like that. Seductive, soothing, relaxing. . . then -- WHAMMO!

Here are some balmy-weather pit-falls to watch out for. And some defensive strategies. The EYES Have It

Two is all we get, and most of us subject our complicated and delicate seeing equipment to a host of abusive practices. The American Association of Ophthalmology has some suggestions for giving eyes the kind of maintenance you'd give, say, to a Hasselblad camera:

Glare. Avoid it. It can cause temporary blindness and ultraviolet rays reflected from a sandy beach can cause real corneal burns. The reaction -- just as with sunburned skin -- can be delayed, but it is painful and potentially dangerous if it is not immediately treated professionally.

Infections. Some come from swimming in algae-filled water, some from insects, some from rubbing impurities in the eye. Irritations from infections often are like those from allergies, wind or over-chlorinated pools. iWhen any irritation persists, victims should get to the ophthalmologist.

Sunglasses. Unless you don't mind befuddling your color perceptions, stick to neutral gray or smoky colors. Green and brown are all right, but avoid yellows, pinks, purples and reds. If you wear contacts, you may still want sunspecs -- and don't forget to give your eyes a rest from contact lenses, too.

Goggles. Wear them when playing games where a batted or racqueted ball can smack an eye with near-bullet force. Several kinds of specially designed eye-protection gear are available. In the EAR

Ear doctors (whose jurisdiction usually includes noses and throats as well) know that in the weeks ahead they are going to see a lot of an often excruciatingly painful ear ailment called, among other things, "swimmer's ear" or "jungle ear."

Dr. David Fairbans, associate clinical professor of otolaryngology at George Washington University Medical School, says this condition, an inflammation of the outer ear, is caused when ear wax does not permit moisture to evaporate. "Ordinarily," he says, "the skin of the ear canal has good resistance, but when it is left moist and it is warm and damp (it provides) perfect conditions for bacteria (most commonly) and fungi to set up housekeeping."

It causes such intense pain, Dr. Fairbanks says, "that sometimes I can even tell on the phone. I ask the patient to push on the triangular cartilage at the front of the ear and when I hear that howl of pain, I know right away . . ."

When it is a fungus that causes the problem there is usually less pain, but a "schlerpy, schloppy sensation." Both conditions usually can be treated easily by a doctor, and in most people, says Dr. Fairbanks, they can be prevented altogether.

Note: If you've every had a punctured eardrum or a mastoid operation, or if the ear is runny or draining, this may NOT be for you. Stop reading and check with your doctor.

For everybody else, the ear can be dried simply after swimming, showering, hairwashing (even at the beauty shop), or even after sweating profusely. The method: Drop an eyedropperful of plain rubbing alcohol (or half alcohol, half white vinager) in the ear. Says Dr. Fairbanks, the alcohol absorbs the water and also kills off the fungus when it washes out. Gesundheit!

People are sneezing this spring who never sneezed before. All those spring showers gave us flowers, all right, along with especially lush pollen-producing trees and grasses, says area allergist Dr. Richad Rosenthal. "All that yellow dust on your windshield and lawn furniture," he says "is giving you your runny nose." For mild cases, he suggests antihistamines and decongestants.

For those of the serious hay fever persuasion, there may be just time enough to get sensitized for the fall pollen festival. Although desensitization traditionally has taken around six months, new products, says Rosenthal, are being tested which may be able to do the job with six weekly injections.

Assistant professor of medicine at Johns Hopkins University in Baltimore and chief of allergy at Fairfax Hospital in Virginia, Rosenthal is always looking for subjects for ongoing allergy research. Interested sufferers should call (703) 573-6500. Summer Sun

The relationship of skin cancer to sunspot activity is a subject of some dispute among dermatologists (who think there might be) and geophysicists (who doubt it). Whatever, there is a large body of evidence pointing to increased risk of skin cancers among people who spend long daily hours in the sun.

There is also, dermatologists will tell you, a strong correlation between lots of sunbathing and wrinkles, particularly of the face and neck. It's easier now to take precautions, with a number of efficient agents on the market for blocking the sun's ultraviolet rays. (For a rating, see the current Consumer's Reports.)

But sunspot activity comes in cycles and we are near the peak of one such cycle this year (and probably for the next two), according to Joe Herman, acting chief of the Space Environment Services branch of the National Oceanic and Atmospheric Administration in Boulder, Colo. But "we feel," Herman says, "that it is unlikely anyone on the ground would notice the difference."

Something that may indeed affect the degree of sunburn, however, is the ozone layer. In fact, daily weather reports (according to meteorologist Melvyn Shapiro) may someday be as able to calculate a summertime "sunburn factor," as they do wind chill in the winter.

New research at the National Center for Atmospheric Research at Boulder has given scientists fascinating new information about how the ozone layer (which filters the sun's dangerous ultraviolet rays) can change along with weather systems.

"If the ozone is cut in half," says Shapiro, "the burning rate is increased by four times." Satelite observations, he says, have dislosed that from one day to the next ozone protection varies over a given area, especially in the spring and fall.

What's more, he says, even an umbrella won't help if there are those high cirrus clouds; then the ultra-violet rays may be reflected so they move horizontally! Creepy Crawlies

Watch out for squirrels and prairie dogs, especially sick ones. Bubonic plauge may not be what it used to be, but it's still around, shows signs of getting worse, and is no laughing matter in the western part of the U.S.

Dr. Allan Barnes of the Plague Branch of the Center for Disease Control in Fort Collins, Colo., says we've been averaging about 15 cases a year since mid '70s, with as much as a 15 percent mortality rate. He attributes the increase to 1) increased populations in Colorado, New Mexico, Utah and Arizona, where the cases tend to cluster (with a few in California) and 2) the "back-to-nature" movement bringing people nearer the animals who carry the fleas that carry the plague.

Ground squirrels, who love to settle near campers and trash-generating communities, cause much of the problem. Prairie dogs, who are dying wholesale of the plague, tend to "amplify" the plague germ's presence. Dr. Barnes warns against camping near animal burrows or getting too friendly with cut little wild animals. Cats, he notes sadly, also have been known to harbor a plague-carrying flea.

Any sick or dead animals spotted in the wilds should be reported immediately to park ranger, camp leader or wildlife authority.

Back East, the problem is ticks, which carry Rocky Mountain (first noted in the Rockies) spotted fever. A vaccine has now been withdrawn for lack of effectiveness), and no new one is expected to be available for five years or so.

Dr. Chad Helmick of the Atlanta CDC office suggests that people in infested area -- mostly in southeast states, especially around the Appalachians -- check themselves every three hours for ticks. "The feeling now is," he said, "that the tick needs to be attached for some hours" in order to transmit the fever-producing organism. If diagnosed correctly, the fever is treatable by antibiotics. There were, two cases last year in Washington, D.C., 75 in Maryland and 90 in Virginia.

Other bug-borne summertime winners include a form of encephalitis (mosquitoes), with which there is a periodic problem and tularemia (rabbit ticks). Furthermore

Watch out for the heat: Dress coolly, drink lots of water, don't get overtired and remember, pets get hot, too: Don't jog with dogs on hot days, for example, or make them walk on hot asphalt surfaces, or leave them in closed cars.

And if the heat doesn't get you, there's always poison ivy, oak and sumac.

Or food poisoning for forgetting to put away the mayo.

Isn't snow wonderful?