The low-fat beef hamburgers to be served at McDonald's restaurants may boost demand for a meat traditionally shunned by many health-conscious eaters.

"Hopefully, it will switch the salad eaters and more nutrition-conscious consumers back to burgers," said Mary Adolf, vice president of promotion at the Beef Industry Council, a trade group.Livestock analysts said that McDonald's Corp.'s low-fat, low-calorie beef burger should have long-term benefits for the beef industry.

Last Wednesday, the Chicago-based fast food chain announced that it was testing the low-fat burgers, which use a seaweed derivative, at outlets in Harrisburg, Pa.

The company said at the time that consumer reaction seems favorable but is difficult to gauge. No decision will be made on expanding testing or going forward with the item as a regular product until next year.

"There are a lot of people who don't go into McDonald's because the quarter-pounder has 400 to 500 calories," said Chuck Levitt, a livestock analyst with Shearson Lehman Bros.

The new low-fat quarter-pound burger has 310 calories including the bun and garnish vs. 410 calories for the regular one.

"It should be beneficial and supportive (to the beef industry) in that it will help overall consumption," said Dick Hummel, analyst with Farmers Grain & Livestock Corp.

Hummel cautioned that initially the new beef may highlight the high-fat content of conventional hamburgers, but over time the new burgers should help the beef industry.

"The important thing is the lean beef," said Dale Huffman, an Auburn University researcher who helped develop the low-fat beef for McDonald's. "The beef industry will have to identify a way to reward producers who produce leaner cattle."

McDonald's spokeswoman Melissa Oakley said the company is indeed buying leaner cuts of beef for the new product, dubbed the Lean Deluxe.

Even those traditionally critical of the fast-food industry hailed McDonald's announcement.

"This is a major breakthrough," said Phil Sokolof, director of the National Heart Savers Association who has campaigned against high cholesterol levels in take-out foods.

"I'm elated this has come. This has been what we have been striving for," Sokolof said.

Oakley, the McDonald's spokeswoman, said the company is using "select" beef, which according to U.S. Agriculture Department standards has less fat than the "choice" grade.

Select beef is traditionally produced from cattle slaughtered at a lighter weight than choice cattle.

In addition to using leaner beef, the low-fat burger includes a seaweed derivative to restore the moisture lost because of the reduced fat content. The derivative amounts to 1 percent or less of the beef content, said Adolf of the Beef Industry Council.

McDonald's would not say how much beef it buys but it is a major consumer, serving millions of hamburgers each year.

In another development, the Agriculture Department will test low-fat ground beef patties in some U.S. schools next spring.

If acceptable, low-fat beef patties would be offered to all school systems for the 1991-92 school year, said Barbara Cope, chief of livestock and feed procurement at the agency's Marketing Service. The department buys about 100 million pounds of ground beef a year for school lunches.