Some have been doing "12s." Others have been doing "10s" mixed in with "15s" and a few "20s."

The numbers are the miles logged in the daily training runs most of those in Sunday's Marine Corps Reserve Marathon have been putting themselves through in the past few weeks and months. In prerace literature sent to all entrants, marathon officials have stressed that no one should dare think of trying to run the grueling 26.2-mile test without conscientious and rigorous preparation.

This is an oft-heard warning. Before the recent New York marathon, a physician wrote to each entrant: "Remember, you have a responsibility to your fellow runners not to tarnish the reputation of this great sport by becoming an unnecessary casualty."

Little question exists that most of Sunday's runners would have become casualties already. The evidence from a sampling of the field suggests that many, whether goaded by the fear of "hitting the wall" or merely heeding the advice of scripture by going "the extra mile," are primed to hear the starting gun Sunday morning at 9 and whisper to themselves, "Cut the baloney and run."

Harold Knapp, 53, a Defense Department analyst who won in his age group last year with a time of 2 hours 54 minutes, ran 20 miles a week for two months. he felt he needed more, so he pushed up to 95 miles a week in the final month. Even then, he has doubts about his performance Sunday.

"In order to do tolerably well," Knapp said, "you need to have a certain amount of mindlessness combined with very intense concentration. The concentration comes in keeping your pace just right, because a few seconds a mile too fast will put you over the threshhold of aerobic running - that is, you will be going at a pace that can't sustain the needed oxygen balance and you quickly become very tired. Two things are important: running at an even pace and then knowing before you run what pace you can sustain. This is especially difficult if you don't know in advance what you're capable of."

Many of Sunday's runners, do know. Frank Stranahan, 55, best known to the sports world as the onetime golfing great, expects to finish at about 3:45. That was his time two weeks ago in New York. Sunday's race will be Stranahan's 65the marathon since he gave up the 19th hole a few years ago for the delights of distance running. Asked if it was a strain to be running a marathon almost on top of another one. Stranahan said, "Not really. One year, I did marathons on three successive weekends. I don't go that fast. My lowest time is 3:18. I could get some speed if I was younger, but I rum because its enjoyable and healthy."

One of those who is younger is Denis Colombant, 35. He is out to break 255, and thereby get back to Bostom. That means he must quality with a sub-3:00 marathon. He ran in Boston last year but suffered excruciating energy fadcout in the last few miles after doing much of the race at a pace of 6.5 minutes a mile. He trudged in a 3:09. Colombant says that, "Frank Shorter is right. To run a marathon, you must forget the previous one - the pain and all. The last miles of the race really hurt. Up to 20 miles, I know what I can do, but after that, there's no way of judging until you do it." Colombant who at 125 pounds and 5-11 enjoys the classic marathon physique, has put in five 20-mile runs in the past two months, as well as "lazy days" of 10 and 15.

Compared with that rigor, James Fallows, President Carter's speechwriter, has been winging it. "I've been getting ready in an inferior way," Fallows admits. "I decided only seven weeks ago to run. I planned to go 13 miles a day to get ready, but in fact I've been doing only nine a day. And that's just for five days a week."

As a Harvard undergraduate in 1969, Fallows ran in Boston and finished in a respectable 3:12.Much like his current boss, Fallows is confident that he can take in stride whatever lays down the road. He speaks of a psychological comfort that few others in the race are likely to enjoy: companionship. "My brother, who did Boston last spring, is coming down and he will be running with me. I think it will be much easier to cruise along together."

Another planning on cruising, as against the near sprinting of the front-runners, is Rep. Lionel van Deerlin (D-Calif). He is a first-time marathoner but with a difference: he once ran a 50-mile race, the annual event along the C&O Canal. "It's true that the 50-miler is an agony thing," says van Deerlin, who has run for office in eight congressional races and won every time.

"But you can walk and eat along the way. In a regular marathon, you can't do that without breaking your rhythm. On Sunday, I'd just like to finish between four and five hours. That won't be too bad. What I'm banking on is that the Pentagon has lured a lot of its armchair colonels into entering the race, so that maybe guys like me who come in after four hours won't be shamed."

If the colonels won't be showing up the politicians , both groups may find themselve unserved by some of the women runners. The favored among the latter is Sue mallory, 23, a graduate student in physiology at Ohio State University. Mallory, whose time of 2:56 led among the women last year, says that she and the other women have a slight advantage over men because the crowds really notice and appreciate us. We stand out. The extra cheering that we get helps us to keep going. I also wear a shirt that says 'Human Energy,' and I've noticed that people like that too."

Whether Sunday's 3,000 runners need to be clocked by a stopwatch or a calendar, many will dine tonight on the traditional "last meal" dish of pasta. A current theory - it is no more than that - is that leading up on carbohydrates in the three days before the race provides a storehouse of energy to aid the body when it depletes at 18 or 20 miles. Some runners dispute this notion particularly vegetarians and fruitarians who belive that their diet is superior.

Sunday at 9, at the Iwo Jima War Memorial where the long-distance battle will commence, theories about training and food won't count. Tarzan Brown a Narragansett Indian who in the 1930s became on of the world's greatest runners, prepared for marathons by no more than a lope down to the corner saloon to carouse away the evening. Brown's legendary method worked, at least for him: not only was he a winner at Boston but he once ran and won marathons on successive days, and did so with a double hernia.

If there is a legend in Sunday's race, it is pete Strudwick. He is the Californian who runs in marathons despite having no feet. Suffering a birth defect, he wears specially designed shoes. Last year in Washington, he finished under five hours. When runners tire in marathons, they sometimes look to others to "bring me in." Tomorrow, for those who reach 22 miles and feel they have had it, perhaps they can wait for Pete Strudwick to come by, and follow him on in.

If that doesn't work, there is still the chance to dig deep into ones own emotional reserves. David Gottlieb, a veteran marathoner and a poet, is likely to be thinking of a poem he wrote a few years ago, "The Pain Can't Capture Me."

When I know I can't pursue the pace any longer.

I see the finish and my cometitors who would best or chase me for place.

Queuing up reserves.

I summon my mystic muse

Who through her charm entrances [WORLD ILLEGIBLE]

Forgetting jatigue, she and I flow to the finish -

An easy leaf on the rippling brook.