It was as if De Beers Ltd. suddenly dumped most of its diamonds on the world market at once.

"There's just too much here," fumed Ralph Newman, owner of the Abraham Lincoln Book Shop in Chicago and the foremost dealer in Lincolniana in the country. "The market can't absorb it all."

Sotheby Parke Bernet was not auctioning off diamonds yesterday, but it might as well have been. To dealers and collectos alike, the Roy P. Crocker Collection of Lincolniana and other presidential memorabilia was a motherlode. And in about four hours of staccato selling, Sotheby president John Marion dismantled what many considered to be the last great private collection of Lincolniana in the country.

"This may be the last big Lincoln sale we're going to see," Newman observed after dropping $21,000 for the sales contract written by Lincoln for the purchase of his in Springfield, Ill. "Most of it is going out of circulation to institutions and private hands."

Crocker amassed the 349-piece collection while he built and ran the Lincoln Savings and Loan Association from 1926 until his death two years ago. His son, Donald W. Crocker, decided to sell the collection after his father died.

When the dust had settled yesterday, the collection had realized over $439,000, nearly $100,000 more than predicted by Sotheby cataloguer Jerry Patterson.

"Lincoln is always in," explained one buyer.

It did not end with a whimper. Television cameras and reporters joined over 100 bidders in the elegant third floor auction room at Sotheby's to see who would walk off with the stovepipe hat that Lincoln allegedly wore the night he was assassinated at Ford's Theater and the opera glasses he carried with him at the time.

They wanted to see who would buy a copy of the operative legislative document of the 13th Amendment, signed by Lincoln, 38 senators and 115 representatives; the Riggs bank check for one gold dollar that Lincoln wrote out to his son, Tad, and the 134 other Lincoln items dealing with the presidency.

The big spender yesterday was Malcolm S. Forbes, the irascible publisher of Forbes magazine known best at auction houses for his insatiable appetite for the dazzling Faberge jeweled eggs that once belonged to the Romanov czars.

Forbes, who bills his magazine as "the capitalist tool," sent his son, Malcolm Jr., to Sotheby's with a mandate to buy. Somewhere around $100,000 later, the young man stopped, having left Newman and other well-known dealers in the dust.

Steve, as Malcolm Jr. is known, batted his eyes a few times and bought the 13th Amendment document for $35,000, the opera glasses for $24,000, Lincoln's hat for $10,000 and the check to "Master Tad," for $12,000.

No, young Forbes said, he had no plans to wear the hat or use the opera glasses. He didn't want to get shot, and, besides, his father said all of the acquisitions would join the Faberge eggs on display in the lobby of Forbes magazine.

The elder Forbes, according to his son, already has a Lincoln collection worth well over $1 million and what he considers to be the finest private presidential collection in the country.

Experts like Newman snorted at the hat and other items in the collection which, they felt, lacked pedigree. The hat didn't have the "provenance," or proof of past ownership, to satisfy them that it was the real thing. Even Patterson conceded that its provenance was not strong.

"Someone tells someone else that it's the hat Lincoln wore at Ford's Theater, and from then on, it's billed that way," scoffed Maury Bromsen, a Lincolniana collector from Boston.

The young Forbes was also less than impressed with the provenance of the hat during the morning auction session. But after buying it in the afternoon for $10,000, his attitude changed. "It's as verifiable as you can get under the circumstances," he concluded.

Crocker didn't stop at Abraham Lincoln. George Washington, Thomas Jefferson, John Quincy Adams, Andrew Jackson, and Harry Truman were some of the other presidents represented in the collection. And interspersed as well were some truly bizarre signatures for the autograph addict.

Patterson was particularly pleased to see that a check from Alexander Graham Bell to Helen Keller sold for $800, over four times the amount he had predicted.

A marvelous character identified in the catalogue only as Waldo C. Moore managed to obtain autographs from famous people by giving them a penny and then asking them to write a check for that amount, according to Patterson. aMoore persuaded the likes of Annie Oakley and Harry Houdini to pen him one-cent checks. But the thrifty George Bernard Shaw sent Moore back a check for only half a penny.

The Annie Oakley check sold for $650, exactly twice what a Napoleon signature drew and $200 more than Percy Bysshe Shelley.

The surprise of the day was Herbert Hoover. Newman paid $3,250 for a check made out by Hoover to a bank. Despite guffaws from philistines who didn't know any better. Newman maintained that Hoover is definitely hot.

"All of his checks are in the Hoover library," he said. "There just aren't any left around."

Checks written by modern presidents are often worth more than earlier ones, added Daniel Weinberg, Newman's associate. "In these days of the imperial presidency, no one sits around writing personal checks any more, but George Washington had to sit down and write a lot of them himself.