Every autumn the great yachts of the East descend on Annapolis to compete for one of the jewels in the coastwide ocean racing crown -- the Chesapeake Fall Series.

This season they raced on three successive breezy October Saturdays, massing in a show of ballooning white sails and glittering glass hulls off the mouth of the Severn River.

There was Tatoosh from New York, the eventual winner; the pitch-black Running Tide, at home in the Bay; sleek red Immigrant; the dark blue Albemarle Pippin; Tabasco and Wunder Bear and 90 other state-of-the-art speedsters.

And lo! What's this?

Crashing along the windward edge of the A-class starting line, where the big boys congregate, came an upstart.

A rented yacht.

There was a crew of eight aboard, seven of whom had never raced a big boat before. In fact, five had never even sailed before this year. Thus armed they took off in a puff last spring in their leased boat and campaigned the season away.

Yacht racing is supposed to be the last bastion of the white ducks and blue crowd, now that tennis has turned into a playpen for overpaid, neurotic teenagers.

Yet here was John on the jib-sheet winch, sipping coffee and reading the morning paper five minutes before the start of the last big race of the year.

"Watch that boat to the leeward," a shipmate shouted.

"Leeward," muttered John."Which way is that?"

The crew of this jolly yacht set out to prove in the fall series that you don't have to be rich, refined or even yachty to enjoy yacht racing at its peak.

Just nervy.

The skipper is a Washington area businessman who asked for the sake of propriety that his identity be kept confidential. Call him Ahab.

Four years ago he decided that sailing would be a nice sport to pursue and bought a little boat. The next year he bought a bigger boat, but he never raced either one. Then last spring he found a $100,000-plus racer no one was using and he offered a spring-summer-fall lease to the owner.

For reasons incomprehensible to the average mind the owner said yes, and agreed to a preposterously low price that came out to about one-third of the yearly upkeep of the boat.

It all has to do with tax write-offs, depreciation and other high-finance mysteries, and the end effect was that for pocket money Ahab had a reasonably well-equipped boat that could race with the fastest, most expensive boats around. All he needed was someone to sail her.

He found Billy, his only crew member with ocean racing experience, and Billy gathered a bunch of his pals who had strong backs and willing spirits and they were off to the races.

They raced the spring series and the Wednesday night series on the Bay, and when the apex of the Bay racing season arrived last month they were ready. aSort of.

On the first fall series race they managed to miss the start altogether. "We thought there would be two starts for the A-class boats, A1 and A2.

When the gun went off they all took off, and we were standing there scratching our heads," explained the navigator. "We went home."

The second fall series race was better, as the neophytes crossed the line with the pack and managed even "to beat three or four boats," said Ahab.

Then two weeks ago came the final assault on the prickly standards of the yachting world.

Ahab thought he had a fine spot on the starting line 20 seconds before the gun, but one of the competing skippers had another plan. He came hard-charging to an upwind spot and began pushing Ahab downwind.

What he did'nt reckon on was Ahab's minimal investment. "Coming up," shouted Billy, and Ahab steered for the intruder's beam.

A shocked look crossed the newcomer's face and he veered downwind and out of the pack.

Our stalwarts sailed their rented boat hard and they sailed it well. Billy wanted halyard tension on the spinnaker at one point. The winch was straining already. The crew told him so.

"Just keep winching," said Billy. "Rip it off the deck if you have to. It's not our boat. Not after today, anyway."

They didn't beat three or four boats that final race. They beat six or seven. And those six or seven had spent fortunes not to get beaten.

When Ahab motored back to the slip he took a look around, said farewell to his rented yacht and went home. The next day the lease would be up and his headaches had never begun.

Good memories were all that lingered on. ONE LAST RACE The fall series is over, but one major race remains on the Chesapeake before the big boats head for Florida and the Southern Ocean Racing Circuit.

This weekend there will be the overnight season-ender, the Skipper's Race, which begins Saturday off Annapolis.

The end-of-the-season marks a fine time, according to Ahab, for would-be racing yacht leasers to start hunting around. "It's amazing what you can bargain people down to," he said," when their boats are locked in the ice in January."