Approximately 2,000 runners will tighten their shoelaces, rub linament on their legs and try to eliminate the concept of pain from their minds this morning.

They will be competing in the ninth stage of the Schlitz Light National Marathon Series, a 15-race event that awards individual winners with college scholarships and donates a portion of the entry fees to the United States Olympic team.

Today's race, a 26.2-mile event sponsored in conjunction with the Potomac Valley Seniors Track Club, will start and end at the Lakeforest Mall in Gaithersburg, at 8 a.m. A half-marathon (13.1 miles) race will be run at the same time as the 26-miler, with a quarter-marathon (6.6 miles) getting underway 15 minutes later.

The top 50 men and first 50 women finishers will qualify for the Schlitz Light National Finals in Tampa, Fla., Dec. 16. Both the first male and female college finisher in today's race will be awarded a $500 scholarship.

Notable among the absentees for today's race will be 1976 Olympian Garry Bjorklund, who won four of the first eight races of the series.No other series winners will compete, either.

"We regard this race as more of a warmup, an event that will prepare people for other marathons," said race director Dick Good, himself a marathoner.

Good added: "The previous marathon winners have already qualified for the final and thus have decided to pass up this week's race. The weather here is still too warm for a major effort."

Good said he expects most of the competitors to be local runners, with a few out-of-town entrants included.

Males finishing in under three hours and females plus males over 40 in less than 3 1/2 hours will automatically qualify for the next Boston marathon.

Good said the Gaithersburg route is flat compared with the last course he competed on. Nobody can debate that remark since Good last ran in the Pikes Peak marathon.

"This is slightly more difficult than the Boston marathon course," said Good, "Boston is basically downhill, forcing you to run faster than you would like to at the start then tiring you out later. This one is more or less flat, with some gently rolling hills along the route, requiring a more steady pace."