Sunday, an estimated 275,000 people will crowd the banks of the Charles River for one of the following events:

A. A World Cup soccer game.

B. Easter Mass at the Vatican.

C. A Prince concert.

D. The 24th Annual Head of the Charles Regatta.

Since the World Cup won't be held in the United States until 1992, Easter is six months away and Prince is in Worcester, there's only one answer.

The Head--Boston's annual rite of fall.

This year, the Head will feature more than 3500 rowers in 840 boats, competing in a total of 16 individual and crew races. The course begins at the Boston University Bridge and spans three miles to the finish line near the Herter Center on Soldiers Field Road.

The first race, the Club Singles, is slated for 8:40 a.m. Fourteen races and seven hours later, the Championship Eights event will close out the day's schedule.

All results of the races will be officially announced at the Cambridge Boat House on Memorial Drive.

The regatta, which 400 volunteers have helped to organize, will feature the world's best rowers, including some Olympic medalists.

Andy Sudduth '83, who captured a silver medal in the single sculling in the 1984 Olympics, and Anne Marden, a silver medalist in women's sculling in Seoul, have entered the Regatta. Marden is the defending champion in the Women's Championship Single.

Regatta organizers hoped that the world-class East German team would participate in this year's events, but the East Germans have decided not to race because they are on a one-month vacation after a successful performance in Seoul.

"The entire team takes one month off together," said Anna P. Jones, publicity spokesperson for the Head. "They're cooling out."

The U.S. Men's Eight will not race as an entire crew. Four members of the crew, however, will row for the Penn Athletic Club.

"These guys haven't rowed together since Seoul," Jones said. "If they raced together [at the Head], they're inviting challengers to defeat them. They've got everything to do."

The U.S. Women's Lightweight Four will race together as a team and for the first time, the crew will officially represent the U.S. Last year, the crew was listed under the Groton School.

Unlike normal racing conditons, the winner of each event is determined by time. Boats will start from the B.U. Bridge every 10 seconds. There is no head-to-head at the Head. It's just the boat battling the clock and the Charles' winding course.

Yet despite the race against time, the action on the river probably will still get heated, especially when faster boats gain on slower boats and when all the boats try to challenge for inside position on the river, Jones said.

Fatal Stroke

"Coxswains go out of their minds. It's a coxswain's course." Jones said. "Every boat needs the finesse to thread the course and pass other boats. Everone wants to be on the inside curve."

This year's Head will also feature a new event, the Grand Masters Singles. With the rise of more rowers in older age brackets, Jones said, organizers have created the Grand Masters for rowers aged 50 to 60.

The Veterans Singles includes any rower 60 and over. Tom Crosby, a 87-year old rower, is the oldest Head participant.

The biggest concern for reggatta organizers is the same concern that has plagued the Head in past years--the party scene on the river's banks. Such a scene detracts from the nature of the regatta, Jones said.

"It's pretty ugly," Jones said, "The Metropolitan District Commission has juridiction over the banks and will crack down."

Another concern is how to safely manuever 840 boats from the water to the banks. Magazine Beach will be the port of call for the boats, which, according to Jones, are worth from $3000 to $10,000. Add the fact that these boats are not that flexible when it's easy to see why such a feat must be smoothly run.

If boats misjudge their landing, Jones said, they could be penalized for being on the course when they shouldn't have. Penalties add time to a boat's final time.

And time is what every boat wants to conquer at the Head.