A TRAVELER who becomes ill away from home can feel awfully helpless when trying to locate a doctor. On trips abroad, the State Department recommends contacting a U.S. consular officer, who ''will atempt to locate appropriate medical services'' and help notify family or freinds, if necessary. Most U.S. embassies try to maintain a list of English-speaking doctors and dentists.

If illness strikes on a trip in this country, experienced travelers suggest calling a member of a professional or service organization to which you belong (Rotary, for example) for help in getting the name of a doctor. Such group members go out of their way to assist a visiting colleague, says a seasoned business traveler.

The State Department offers other health tips that are applicable for both foreign and U.S. destinations:

* Pack an ample supply of any essential medication. Keep it in its original container. Take along the doctor's prescription.

* Take along an extra pair of eyeglasses. (Hand carry them and medication in case of lost luggage.)

* Travelers with allergies, reactions to certain medicines or other unique medical problems should consider wearing a "medical alert" bracelet.

* Don't forget to take the policy identity card for medical insurance purposes. (The State Department warns senior citizens going abroad that Social Security Medicare programs generally do not provide for payment of hospital and medical services outside the U.S.)

In just a few weeks, the weather will turn comfortably cool and the trees will be ablaze in color -- a delightful time for a bicycle tour, on your own or with an organized group.

The League of American Wheelman, a Baltimore-based national organization of 20,000 cyclists and 500 cycling clubs, has compiled a list of 97 commercial tour sponsors worldwide, 30 of whom offer trips from two days to two weeks in the United States and Canada. For the fall foliage, tours are available in Maine, Vermont, New Hampshire, New York and Pennsylvania from an average of $70 to $700 per person.

For a copy of the tour sponsor list, send a stamped, self-addressed, legal-sized envelope to League of American Wheelmen, P.O. Box 988, Baltimore, Md. 21203.

In the high Atlas Mountains of southern Morocco, the Ait Hadiddou tribe of the Berbers gather each fall at a three-day bazaar, partly to trade but also, in the case of the unmarried, to seek a spouse at the Imilchil Betrothal Fair.

On Sept. 18, Piotr Kostrzewski of Arlington, a former Peace Corps volunteer who taught English in Morocco for two years, plans to lead a 10-day air and Land Rover trip to this seldom-visited ceremony in a windswept valley. En route, travelers will crosscross the Atlas range and touch briefly at an oasis on the edge of the Sahara Desert. They will complete their journey with a stay in the city of Marrakech, returning home Sept. 28.

Kostrzewski points out that the Berbers have changed little over the ages, many still living in mud-walled fortresses. At fair time, they come from all over the Atlas mountains with their sheep, donkeys and camels to trade rugs, silver jewelry, tools and domestic utensils. At the betrothal rites, women have equality with the men in picking or rejecting a mate.

This is the first tour offered by the Arabic-speaking Kostrzewski, 30, a one-time editor of medical and scientific publications. He formed Cross Cultural Adventures to develop trips aimed at presenting "the way of life of the peoples of a country." The group is limited to 12 people, and the cost is expected to be between $1,000 to $1,200 (based on size of group) plus about $623 for airfare via TWA from New York to London and Royal Air Maroc to Marrakech.

Accommodations will be in first-class hotels, except for the day and a half at the fair, where visitors will share the large black tents set up by the government for the event. For information: Cross Cultural Adventures, P.O. Box 3285, Arlington, Va. 22203, or 243-7194.

Through Oct. 30, Amtrak passengers can travel from any point on the 24,000-mile rail system to a second point and back for $225 (from ages 2-11, half-fare is $112.50). The one big catch is that no stopovers are allowed between the two points.

Nevertheless, for a round trip between Washington and Los Angeles, the saving is substantial. The current round-trip excursion is $470, more than twice Amtrak's "Anywhere Fare." Just don't get off for a day in Albuquerque on the way unless you are willing to buy an extra Albuquerque-to-Los Angeles ticket.

To see more of the country, take a northern route west and a southern one back.