Georgetown University oarsmen will plunge into the major leagues of rowing this coming week, competing for the first time in an eight-man boat race at the annual Henley Regatta, the genteel carnival of world class crew.

The Georgetown eight of mainly middleweights represents the best of the university's rowing association, according to Coach John Forster. The crew is entered in the the Ladies' Challenge Plate, a 32-team contest that dates back to 1845. In terms of prestige, "Ladies" ranks just below the Grand Challenge Cup.

The race covers a lovely stretch of the Thames River not far from London, on a course of 1 mile 550 yards. The record is 6 minutes 24 seconds, set in 1976 by Trinity College of Hartford, Conn. That is two minutes faster than the first victory time so long ago.

Georgetown had a four-man crew beaten in a semifinal three years ago. But this year's entry puts the university into competition with some of the best-known names in the sport, including crews from Harvard, Yale and the University of London, which is favored. Victory against so stiff a group of challengers is a long-shot for the Georgetown oarsmen, even Forster acknowledges. Still, the 36-year-old coach is hopeful.

"There is nobody tougher than we are mentally," he said. "We've been improving throughout the season and in a week we'll show the results."

The crews were matched by lots for the opening heat Thursday. The draw was designed to keep the fastest and strongest crews from competing against each other before the semifinals.

The crew Georgetown will face from Bristol University is rated no better than Georgetown itself, which is in the middle of the field.

Whatever happens, taking part in the Henley is a special experience for oarsmen (and women, who were admitted for the first time last year). The regatta was begun in 1839 and soom became the highlight of the British rowing season. It has developed some of the same quality as Wimbledon, a top-flight international sports event marked by a distinctly British style.

One author recently likened Henley to a "Victorian picnic" complete with strawberries and cream, straw boaters and club ties arrayed against a backdrop of quaintly beautiful old houses that line the streets of Henley-on-Thames. Wimbledon and Henley generally coincide (the Regatta runs July 1-4) and are both subject to the vagaries of British weather, currently running somewhat cold and drizzly.

But as a rule, the occasion has a warn summertime feel in spite of the temperature. Unlike its tennis counterpart, Henley has little of the razzle-dazzle of big time professional sports. Eight-man crew in particular is very distinctly a team effort.

There are 54 entries from countries other than Britain, with tough East German crews given a strong shot to prevail in several races. The majority of boats are manned by college students, so Henley remains very much an amateur gathering.

In all, there are 271 crews and scullers entered in this year's races, a record number of participants for the draw. There are nine entries for the Grand Challenge, including Harvard, Cornell, Yale, California (Berkeley), Syracuse, the Charles River Rowing Association, an East German club and two British teams.

The Ladies' Challenge Plate generaly gets the second-best entries of the top rowing competitors, second varsities from places like Yale or teams representing individual colleges at Oxford and Cambridge.

The Georgetown eight comprises one sophomore, four juniors and three seniors. They weigh from 153 to 190 pounds, which puts them at the lighter end of the scale. Forster said the eight were chosen in heats among the members of the Georgetown Rowing Association. The $12,000 price tag for the trip was raised by the rowers and the university.

Forster said that crew at Georgetown began in 1890 but it is only lately that the school has felt ready to compete at the higher levels of its class. The "Ladies" is a big step up.