Hospitals are in for a growing dose of competition from alternative facilities, such as birthing centers and hospices, reports a new forecast of health care trends by Arthur Andersen & Co. and the American College of Hospital Administrators.

The study, "Health Care in the 1990s," surveyed a panel of 1,000 professionals from all sectors of the health care industry. An overwhelming majority of those surveyed believe that non-hospital centers will be "very successful" or "slightly successful" by 1990.

The following types of alternative centers were most often cited by panelists as likely successful hospital competitors: free-standing outpatient centers (98 percent), surgery centers (97 percent), home health agencies (96 percent), diagnostic centers (96 percent), minor-emergency centers (95 percent), hospices (90 percent) and birthing centers (85 percent).

Competition in health care will become more like competition in traditional business markets by the 1990s, predicts the report, with cost joining quality as an increasingly important factor. "Natural" Junk Food

A food billed as "natural" isn't necessarily nutritious, warns the Center for Science in the Public Interest (CSPI) in sin- gling out ten products for its Best and Worst awards.

CSPI's Best Five were picked for their nutrients and high-fiber, low-sugar, low-sodium content. They include whole wheat pasta offered by manufacturers such as De Bole's, Johnson's and Westbrae; wheat berries (the whole kernel of wheat), often available from bulk bins at bargain prices; Colombo nonfat yogurt; Tree of Life boysenberry spread made only from fruit with no added sweetener; and mung beans, ideal for growing bean sprouts.

The Worst Five, which could "hold their own against any junk food," include Health Valley Lean Living Spinach-Mushroom Casserole (30 grams of fat per 7.5-ounce entree); Hain Wild Cherry Gel Dessert Mix ("a sanitized version of the junk food classic Jell-O"); sea salt (no less a contributor to high blood pressure than table salt); Joan's Natural Honey Bran Carob Bar; and Hain Pure Coconut Oil (86 percent saturated fat -- more than butterfat or lard). A Mother's Touch

Can a mother judge whether or not her child has a fever without using a thermometer? A new study suggests that she can if her youngster is 2 years old or younger and has a fever above 102 degrees.

Researchers from the University of Connecticut's School of Medicine studied 303 children, ages five days to 15 years, treated at Hartford Hospital for non-emergency medical care. Only 27 children had their temperatures taken at home before coming to the hospital.

A little more than half the time, mothers correctly detected fevers in their children, the researchers report in the American Journal of Diseases in Children. That's just slightly better than the expected accuracy rate if left to chance. But the mothers' accuracy rose to 90 percent if the children were 2 years old or younger and had fevers of 102.2 or more. Mothers were even better at identifying no fever in their children -- in that case they were right 94 percent of the time.

The most common technique used to gauge fever was feeling the child's forehead and face. Yet the findings also suggest that touching a child's abdomen or torso is a slightly more accurate method of assessing body temperature. Selenium-Cancer Connection

Middle-aged people with very low blood levels of selenium have a strong risk of developing some types of cancer -- particularly gastrointestinal cancer -- concludes a new study published in the American Journal of Epidemiology.

More than 8,000 Finnish men and women, ages 31 to 59, participated in the six-year study. None had cancer when the study began in 1972. By 1977, 43 people had died of cancer, and by 1978, another 85 had been hospitalized for cancer treatment.

Researchers compared the participants who developed cancer with those of the same age, sex and cancer risk factors -- including smoking habits -- who didn't develop the disease. A significant difference in selenium blood levels emerged. Those who died of cancer had the lowest levels of selenium -- a trace element found in high quantities in fish and mushrooms. Those who developed cancer, but did not succumb to the disease, had slightly higher blood selenium levels. However, this group still showed significantly lower blood levels of selenium than the control group without cancer.

In this country, the National Research Council advises consuming 50 to 200 micrograms a day of selenium, which can be met by eating selenium-rich foods such as seafood, kidney, liver, meat and -- to a lesser extent -- grains.