For almost 6,000 of the 9,100 entrants, Sunday's Marine Corps Marathon will be their first marathon. For one veteran, Dean Matthews, it will also be an excellent opportunity to test an injury that has prevented him from running competitively for two years.

Matthews, 26, suffered a sciatic nerve injury a few months after he won the 1979 Honolulu Marathon, in 2:16.11. Earlier that year, he had finished 12th in the Boston marathon, running 2:14.48.

"There is a winners-only attitude at the New York Marathon (which was run Sunday) and a lot of pressure from promoters. I don't think I'm physically and mentally prepared to get into that kind of race," Matthews said by telephone yesterday from his home in Atlanta.

"The Marine Corps Marathon is a very unique race. It's the first time I've ever paid my own entry fee. It's a low-key race."

Matthews has not competed in a marathon since his injury. He ran 29:02 for 10 kilometers in the Peachtree Road Race earlier this summer and finished 13th in the tough Falmouth, Mass., 7.5-mile run.

Matthews will be one of the favorites in the Marine Corps race. Another top competitor will be Thomas Blumer of Cincinnati, a sub-2:20 performer who beat Bill Rodgers in a 10-kilometer race in South Bend, Ind., two weeks ago.

Defending champion Michael Hurd, who ran 2:15 in a race in Belgium this summer, also is back. Hurd, 35, competes for the British Royal Air Force and will lead a strong contingent in an attempt to win the military team contest.

Among the other sub-2:20 runners entered are Hank Pfeifle of Maine and Jack Coakley of Massachusetts. Rosalie Geuss of Arlington, who has ran a 2:50 marathon, is the women's favorite.