Frank Shorer finished 12th in last Sunday's New York City Marathon, but was euphoric after what he considered his best race at the distance in two years. The winner of the Olympic gold medal in the marathon at Munich in 1972 and the silver medal at Montreal in 1976 apparently has recuperated satisfactory from surgery on his left foot and is on the road to Moscow in 1980.

Shorter's time for the 26-mile, 385-yard course from the Staten Island toll plaza of the Verrazano-Narrows Bridge, through streets of all five of New York's boroughs to Central Park, was 2 hours 19 minutes 32 seconds. More significant, he covered the final six miles in less than 30 minutes surging from 29th place after 20 miles.

Last year the popular Yale alumnus pulled up lame on a tender and swollen left leg, dropping out at the 15-mile point - the Queensboro Bridge, which spans the East River and connects Queens and Marahattan at 59th Street. He had faltered at roughly the same spot in 1976.

Shorter finished 23rd in his first attempt at the fabled Boston Marathon in April, doing 2:18:15. Boston's Hopkinton-to-Copley Square route is hillier and more rugged than New York's, but the cool weather this year was much more condusive to good times than New York's 64-degree heat and 60 percent humidity.

Less than two weeks later on April 26, Shorter underwent surgery for a bone spur, the latest in a long series of ailments. In July he started light workouts, but only for 15 minutes a day. On September 1, he ran 10 miles for the first time since the operation. His interval training was limited.

"Any coach could look at my time for the last six miles and say I didn't go out fast enough, but I just wanted to finish biomechanically sound," Shorter said after the massive New York race.

"I bet I was in 200th place after the first mile. The others went out too fast. I wanted a nice, easy pace."

Garry Bjorklund, Englishman Ian Thompson, and New Zealander Kevin Ryan dictated a brutal early pace - 49 minutes for the first 10 miles - which winner Bill Rodgers kept up with reluctantly, even though he considered it "insane" for the warm, muggy day. Shorter stayed back in the pack, running within himself.

He remembered the painful cramps he suffered halfway through the Boston Marathon, undoubtedly the result of a training schedule curtailed by injury. He didn't want that to happen again, and didn't want to drop out ignominiously. He ran a controlled race and finished fresh.

"I just wanted to get by the 59th Street Bridge, finally," said Shorter, who celebrated his 31st birthday on Tuesday.

"The big pidgeon in the sky has been dumping on me for so long now, I figured anything I did after 59th Street was gravey. I didgured anything I did after 59th Street was gravey. I'm happy because I don't feel decimated. I know now that I'm in good enough shape to run hard and not feel awful afterwards. This is the best I've felt in two year."

Shorter - worse '72 Olympic victory, the first by an American since 1908, is credited by many with starting the still growing marathon craze in this country - remains a favorite even if Rogers is the people's choice. He was warmly cheered by the crowds, estimated by New York Police at nearly 2 million, who lined the pot-hole-scarred pavement of the five boroughs.

"The people were just great. No razzers in Brooklyn this year," said Shorter, the former medical student who now runs a sporting goods business in Boulder, Colo., that supports athletes in training. "Last year a guy on a bicycle followed me all the way through Brooklyn screaming, 'You used to be my hero. What happened to you?'"

Rodgers, who needs only an Olympic gold medal to complete his sweep of the world's most prestigious marathons, expects Shorter to be one of his cheif rivals in 1980.

"I know Frank as a competitor," Rodgers said after his third consecutive New York victory. "If his leg holds together, he'll be there in Moscow giving us all a run."

Shorter finished second to East German Waldemar Cierpinski's Olympic record of 2:09:55 at Montreal, pretzeling with cramps at the finish line on one of the rainy days he despises. Rodgers, injured at the time, finished 40th, a crushing personal disappointment.

Rodgers, 30, has asserted himslef as the indisputable No. 1 marathoner in the world by winning all five races he has entered since Boston in 1977, where he dropped out after 20 miles in the heat that in the past has tortured him as much as rain does Shorter.

Five weeks after that, he won in Amsterdam. Starting last autumn, he captured the three most internationally prominent annual marathons - New York, Fukuoka in Japan, and Boston (which he first won in 1975) - within six monthss, an achievement unsurpassed in marathoning history. Now New York again.

Since the beginning of 1977, Rodgers has won 50 of the 55 road races of 10,000 meters or more that he has entered.

Rodgers considers Bjorklund, 27, the former university of Minnesota distance man who ran the 10,000 meters in the 1976 Olympics, his greatest rival in the immediate future. Bjorklund duled him for 15 miles in New York - as he did a year ago - but paid for setting the torrid early pace and finished 77th in 2:29:58.

"When Garry gets a little more experience and a cool day, he's going to be the best in the world," predicted Rodgers. "He's so strong, he's going to be unbeatable."

The tall, sturdy Bjorklund, who expects to be both 10,000 meter and marathon man in Moscow, won the Maryland Marathon in Baltimore last winter in 2:13:46. CAPTION:

Picture, The field of more than 11,000 participants in New York marathon gets under way. It served as comeback for Frank Shorter, AP