The Dow Jones industrial average lost 49.26 points to close at 6,806.54, having surrendered an early 20-point gain that briefly put the blue-chip barometer within 10 points of a new record.
Decliners outnumbered advancers by an 8-to-7 margin on the New York Stock Exchange, with 1,172 up, 1,340 down and 825 unchanged.
NYSE volume totaled 467.56 million shares vs. 538.62 million Friday. The Standard & Poor's 500-stock list fell 4.11 to 785.45, and the NYSE composite index fell 1.45 to 412.35. Both measures, dominated by larger companies, had closed at record highs on Friday.
The Nasdaq composite index fell 22.32 to 1,335.39, but the American Stock Exchange composite index rose 1.23 to 587.84.
Bonds were slightly lower, lifting the yield on the 30-year Treasury bond - a key determinant of corporate and consumer borrowing costs - from late Friday's 6.69 percent to about 6.70 percent.
Networking equipment maker 3Com warned today that earnings for its current quarter will be disappointing. 3Com shares tumbled as the second most active Nasdaq issue after rival Cisco Systems, which also plunged.
Other technology shares also pulled back. IBM continued to stagger in the aftermath of its fourth-quarter earnings report, and Nasdaq leaders such as Intel, Microsoft, Dell Computer and U.S. Robotics fell sharply.