At 10:30 Sunday morning, a gun will sound at the toll plaza on the Staten Island side of the Verrazano Narrows Bridge, and 5,000 people will run from the scene of the shooting, across the majestic two-mile span into Brooklyn.

Most will not stop until they have followed a painted blue line for 26 miles 385 yards, through five boroughs and across four more bridges, to the Tavern On The Green in Manhattan's Central Park.

That is the route of the New York City Marathon, which, in just eight years against incalculable odds, has become one of the world's most distinctive and popular road races - an important event for both recreational runners and world-class marathoners.

This year the suddenly chic "run through the city" - which requires shutting 300 intersections to autos and pedestrians and two drawbridges to ships - has attracted 5,000 entries, including four of the top six finishers in 1976 Olympic marathon: Americans Frank Shorter (second, behind East German Waldemar Cierpinski) and Don Kardong, Finland's Lasse Viren and Canadian Jerome Drayton, winner of the venerable Boston Marathon in April.

Shorter, the 1972 Olympic gold medalist who finished second to Bill Rodgers here last year, is not totally fit. He had a cortisone shot early in the week to relieve a painfully swollen left ankle which has hampered his training.

The favorite is Rodgers, Shorter's chief rival as the premier U.S. marathoner. He has run the two swiftest marathons by an American. 2 hours 9 minutes 55 seconds to win at Boston under unusually favorable wind and weather conditions in 1975, and 2:10:10 here last year, unders cloudy skies with temperatures near 50 degrees. Cool overcast weather is expected again for his defense.

Viren, , , the winner of Olympic gold in the 5,000 and 10,000 meters in both 1972 and 1976 who finished fifth (2:13:10) at Montreal in his first marathon, is reportedly in ggggood shape. Having recovered from ankle surgery that interrupted his training for six months, he ran a half-marathon in Finland in 1:02 earlier this months.

Other contenders include Englishmen Ian Thompson and Ron Hill whose best times of 2:09.12 and 2:09:28 respectively represent the best career efforts of any of the competitors here. Englishman Chris Stewart who challenged Rodgers for 15 miles last year and finished third in 2:13:21, 10 seconds off his best time: and Americans Kardong (best time 2:11:55), Kenny Moore (2:11:36) and 1973-75 champ Tom Fleming (222:12:05).

The women's field includes defending champ Miki Gorman, the 5-foot-1, 89-pound, 42-year-old Japaneses-born Californian, who this year led the women in the Boston Marathon for the third time: Chantal Langlace of France, whose best time of 2:35:15 set the women's record for the marathon last May: and 1975 winner Kim Merritt, the University of Wisconsin student whose 2:37:19 is the American women's record.

The youngest entrant is Wesley Paul, 8, of Columbia, Mo., who has been running since he was three years old. He has run four previous marathons and his father thinnks he can shave 15 minutes off his last best time and break three hours.

The oldest is Lou Gregory, 75, of Pensacola, Fla., who competed in the 1972 Olympic marathon at Los Angeles..

There will be one blind entrant (Joseph Pardo), one with an artificial leg (Richard Traum), and one in a wheelchair, Bob Hall, 25, of Belmont Mass., who won the National Wheelchair Marathon at Boston, went to court to fight a ban here and was granted admission in an agreement negotiated by State Supreme Court Justice Arnold Fraiman, who is running in the race.

Olympians and the thousandsof social-climbing joggers alike, who are entitled to share a dinner of beef bourguignon when they reach the finish line, agree that this race is an amazing triumph of will over red tape and imagination over seemingly unsolvable problems.

More than 40 municipal and private agencies cooperate to make it happen their duties ranging from manning 21 water stations (by the Boy Scouts) to patrolling auto and bicycle traffic and an expected crowd of perhaps a million spectators (New York Police Department) to carpeting the open steel gratisng of the Queensboro Bridge which terrified many runners last year (City Bureau of Bridges).

The deceptively steep approach to Queensboro Bridge about 15 miles into the race provides a mild "Heartbreak Hill" to a course that is generally level. Fast times are anticipated and the best runners will be aiming at the world record of 2:08:33:6 (set by Australian Derek Clayton at Antwerp in 1969) when they line up for that breathtaking start at the Verrazano Narrows.