Don't let the fear of Rocky Mountain spotted fever keep you from visiting the Rockies during your summer vacation. You have far greater chance of contracting the tick-borne disease after a stroll through the woods of McLean or the fields of Gaithersburg.

Sixty percent of the 398 cases reported nationwide this year have occurred in the South Atlantic region of the country - 53 in Maryland and 48 in Virginia - while only three cases have been reported in the entire eight-state western mountain region.

Only one Dermacentor Variaeilis - dog tick - out of every 100 is a carrier of this potential fatal form of typhus, but the threat of the disease is serious enough to make mandatory check for the presence of the hideous little eight legged creature following any warn weather walk in woods or tall grass.

"There are two types of ticks," says Vincent Garagusi, chief of the division of infectious deseases at the Georgetown University Medical Center. "One is the wood tick (Dermacentor Andersoni), found in the Rocky Mountain range area, and the other is the dog tick, found in the East Coast area."

The ticks in this area are the so-called hard back ticks - they crunch when stepped on or squeezed - as oppossed to the so-called soft back ticks of the West. Both varieties are greyish brown and about a quarter-of-an-inch in length.

According to Dr. Sydney Ross, chief of the microbiology section of the Children's Hospital National Medical Center Research Foundation, "In untreated cases" of Rocky Mountain spotted fever (RMSF), "the mortality rate is as high as 30 percent to 40 percent. If you treat it properly, the mortality rate is about five percent. It's more dangerous in adult," he says, "but about 50 percent of the cases are in children."

"The tick probably has to be attached to the person anywherefrom three to eight hours before it can infect man," says Garagusi. "What happens is the rickettsia, the organism that causes Rocky Mountain spotted fever, become active in the body of the tick once the warm blood is sucked into the tick and they begin to multiply. They find their way to the biting part of the (tick's) mouth and then begin to flow into the body."

Ross points out that a "crawling tick is not a dangerous tick," not that you want to leave it crawling around on you. "It has to be imbedded bfefore it does any damage."

The tick burrows under the skin, and that's when removal becomes difficult. Both physicians warn that it is important for two reasons not to crush the tick while it's head is imbedded in the skin: for one thing, crushing it may result in the head breaking off, and it may become necessary to remove the head surgically; and for another, squeezing the tick may result in forcing even more rickettsia into the body.

The best bet is to use tweezers to to gently grasp the tick and slowly, pull it out of the skin. Some persons advocate using a dab of kerosene nail polish remover, or even lighter fluid, to induce the tick to back out wihtout much prodding. A lit cigarette can be used for the same purpose, but that can result in a burn as well as a tick bite.

If the tick was a rickettsia carrier, in 48 hours to 10 days you will experience the first symptoms: headache, pain behind the eyes, general body and muscle aches and a fever that may go as high as 104 degrees.

"During that stage you cannot make a diagnosis," says Ross, because the disease resembles so many others. "But two to three to four days after the onset of the high fever you get the rash, which is the hallmark of the disease. It starts on the palms and soles of the feet and then spreads to the ankles and wrists" and then on to the rest of the body.

Garagusi describes the rash as "little red pimples . . . which become without scratching. "Some people will have a very intense rash and others will have a spotty rash. There're all variety of rashes."

Both Garagusi and Ross stress the importance of seeking help at the first sign of rash. "If it goes untreated you can get frightening complications," involving the heart, kidneys and central nervous system, Ross said.

The chances of recovery are "directly related to the rapidity with which appropriate therapy" - the use of antibiotic - "is initiated," warns Ross, who says that most patients who begin taking the drug in time fully recover in about seven to 10 days with no adverse effects.

What can one do to avoid the discase? Avoid the ticks.

Check your clothing and body, particularly hairy areas, carefully after walks in the woods or long grass. Wear tick repellent, available at most major drug stores, when headed into tick infested areas, and make sure your animals stay free of ticks throughout the season, which can extend into November.

Then there is the business of the disease most often found on the east coast being named for the Rocky Mountains. It seems that the tick-borne fever was first reported in large numbers in the first half of this century among workers in the Bitter Root Valley in the Rocky Mountain area of Montama. They just never got around to renaming it Potomac Fever.