Two-thirds of the original survey map made by two English astronomers, Charles Mason and Jeremiah Dixon in 1767-68, of the boundary between Pennsylvania and Maryland was bought for $360,000 tonight at auction at Christie's. The figure was a world record price for an autographed map.

Outbidding the Library of Congress, which had planned to add the map of the Mason-Dixon Line to its geography and map division, was Malcolm Forbes Jr., president of Forbes magazine and the son of the magazine's founder.

"This is one of the most important documents in American history. I plan to loan it to Princeton University, which owns the other third of the map," said Forbes.

A broadside reproducing the Declaration of Independence, which was on deposit at the Historical Society of Pennsylvania, sold here tonight for $285,000.

John Flemming, a New York private book dealer, bought the broadside, which is a large printed banner, and he had a curious story to tell. "A Japanese told me to buy it for him . And then last night he called and told me not to buy it. They were worried about international repercussions. So I bought it for myself. Maybe they'll buy it quietly now."

The broadside, one of an unknown number of copies hastily printed July 4, 1776, was the final lot of a small and special sale of colonial American papers from the library of Benjamin Chew (1722-1810), a Pennsylvania patriot and statesman. Descendents of Chew put together the sale, which featured three key lots: The Broadside, the original Mason-Dixon line map and William Penn's charter for his "Holy Experiment," known as Pennsylvania, as well as 22 other lots of material related to Penn and the Mason-Dixon survey.

The sale was to raise money for a family trust, which owned them. The heirs have indicated that they now plan to donate approximately 200,000 manuscript pages of family documents to the Historical Society of Pennsylvania in Philadelphia.

"The papers have become both a shame and an encumbrance. We were unable to maintain them as we should," said John Chew Jr., a family spokesman.

Apparently, the sale raised enough cash to satisfy the trust. Nearly every lot exceeded the pre-sale estimate set by Christie's. And some lots soared beyond the expectations of the house. The total for the entire sale was $837,400, plus a 10 percent buyer's fee. All the lots were sold.

During a suspenseful 38 minutes of bidding, several hundred history buffs sat virtually stock still here in the elegant main salesroom of the London-based auction house. Evening sales are generally reserved only for important paintings. This gave the sale added glamor. With 15 members of the Chew family looking on (this is also unusual), well-heeled buyers competed head on with strapped institutions, yet there was no hysteria and only an occasional joke to break the pace.

In the weeks before the sale, historical societies and libraries scrambled to find angels to help them buy the papers they wanted. The Historical Society of Pennsylvania issued a plea to the community to come up with $90,000, and the Library of Congress and the Maryland Historical Society earmarked funds to use at the sale.

According to James Mooney, head of the Historical Society of Pennsylvania, "when a museum goes into the auction business, you have to have angels. We found a few and we were able to put together a war chest."

All the Pennsylvanians--the Chews, the Historical Society and others--had hoped that the third important document, William Penn's Charter from King Charles II of England issued in 1680-1681 granting Penn's Wood, would end up in Pennsylvania. Alas, it did not. Bringing $48,000 after a momentary bidding war, the charter was sold to an anonymous American bidder.

No one, not even the auction house, knew for sure what the Mason-Dixon curiosa, the letters, maps, ledgers and journals documenting the century-long dispute between Maryland Calverts and Pennsylvania Quakers, would bring. "There's really no way to appraise this material. It's classic Americana," said Ken Nebenzahl, a Chicago dealer at the sale. After all, there is even a song named after the survey line--"Dixie."

The Historical Society of Pennsylvania made out with the key lots of this material. The printed copy of the map, the commissioner's copy, complete with seals, sold for $32,000 to the society. A set of six autographed letters from Charles Dixon to Benjamin Chew, recalling the progress of the survey, brought $12,000. The Historical Society was pleased, judging by the broad smile on Mooney's face.

David Bathurst, president of Christie's in New York and tonight's auctioneer, was also pleased. "The sale moved quickly and briskly. But frankly, as an Englishman, it felt a little funny to be selling this Revolutionary material."