NEW YORK — NBC Sports has inked a four-year extension of its U.S. Open golf pact that will keep the prestige links tournament on the Peacock web through 2003.The deal, signed with the United States Golf Assn., covers the U.S. Open, the U.S. Women’s Open, the U.S. Senior Open and the U.S. Amateur championships. ESPN continues to cover events as the USGA’s exclusive cable outlet. “We feel especially grateful that the USGA has agreed to extend the relationship so far in advance,” said NBC Sports prexy Dick Ebersol in a statement. NBC has a penchant for locking in long-term deals with other top sports franchises such as the Olympics and the NBA. An initial three-year deal, signed in 1995, already was extended by two years, through 1999, and NBC has expanded coverage of the sport. Under the new deal, it will continue to air 16 hours of U.S. Open play, and four to six hours of the three other tourneys.