BEIJING, Jan. 16 - A prominent Chinese lawyer and collector unveiled an old map on Monday that he and some supporters say should topple one of the central tenets of Western civilization: that Europeans were the first to sail around the world and discover America.

The Chinese map, which was drawn in 1763 but has a note on it saying it is a reproduction of a map dated 1418, presents the world as a globe with all the major continents rendered with an exactitude that European maps did not have for at least another century, after Columbus, Da Gama, Magellan, Dias and others had completed their renowned explorations.

But the map got a cool reception from some Chinese scholars and seems unlikely to persuade skeptics that Chinese seamen were the first to round the world.

Liu Gang, a partner in a well-known Beijing law firm and an amateur historian, said Monday that he bought the map for $500 in a Shanghai book store in 2001 and only subsequently discovered its value. He said he had consulted scholars in the field and had done extensive research of his own before deciding to present his findings to the public.

"The main issue is not the map itself," he said at a news conference. "It is the potential of the information in the map to change history."

At issue are the seven voyages of Zheng He, whose ships sailed the Pacific and Indian Oceans from 1405 to 1433. Historical records show that he explored Southeast Asia, India, the Persian Gulf and the east coast of Africa, using navigational techniques and ships that were far ahead of their time.

But a small group of scholars and hobbyists, led by Gavin Menzies, a former British Navy submarine commander, argue that Zheng He traveled much farther than most Chinese and Western scholars say. Notably, Mr. Menzies claims that Zheng He visited America in 1421, 71 years before Columbus arrived there.

His 2003 book, entitled "1421: The Year China Discovered America" (William Morrow/HarperCollins), laid out extensive but widely disputed evidence that Zheng He sailed to the east coast of today's United States in 1421 and may have left settlements in South America.

Mr. Menzies has welcomed Mr. Liu's map as evidence that his theory is correct, and the two have cooperated in efforts to demonstrate its authenticity. Strictly speaking, Mr. Liu credits Zheng He with having navigated and charted the Americas at least several years before Mr. Menzies says he sailed there, though both say that is a minor contradiction.

Zheng He's achievements have been the subject of speculation for years, partly because much of the historical record was destroyed when later Chinese emperors changed their minds about the wisdom of connecting with the outside world. Last year, China's Communist government commemorated the 600th anniversary of Zheng He's better known voyages, but Beijing has not actively promoted the idea that he sailed far beyond Asian and African shores.

If the map genuinely dates to 1418, it reveals knowledge of longitude and latitude and the basic shape of the world, including the fact that it is round, that could not have come from European sources and could have been derived only from Zheng He's voyages, Mr. Liu says.

He referred to 15th-century books and memorial inscriptions and 16th-century maps that credit earlier Chinese discoveries among a variety of indirect evidence to support his thesis.

But Mr. Liu acknowledged that he had no hard evidence of the existence of a 1418 map beyond the word of the mapmaker who said he made the copy in the late 18th century, a time when all of its cartographical achievements would have been commonplace.

Gong Yingyan, a historian at Zhejiang University and a leading map expert, argues that the map is too full of anachronisms to date from the 15th century.

He said, for example, that Chinese cartographers did not use the style of projection seen in Mr. Liu's map - the rendering of a three-dimensional globe on a flat sheet - until after Europeans introduced that technique to the Chinese much later.

The map's Chinese notes about the cultures, religious and racial features of people in the continents of the world also contain vocabulary that would have been unfamiliar to a reader in the early 15th century, he said. He cited the term the map uses for the Western God, which he said was not used until after the Jesuits arrived in China in the 16th century.

"I had high hopes when I first heard about the existence of such a map," Mr. Gong said. "But I can see now that it is an entirely ordinary map that proves nothing."