Jay Murphy scored 30 points and triggered a 57-point second half last night that carried 18th-ranked Boston College to a 92-75 upset of No. 6 St. John's at the Redmen's Alumni Hall in New York.

Boston College, 18-4 overall and 8-3 in the Big East in its first year under former American University coach Gary Williams, trailed at the half, 38-35. The Eagles turned it around with 11 consecutive points from a 44-40 deficit to a 51-44 lead.

St. John's, 20-3 and 9-3 in the league, also lost Jan. 15 at BC, and last lost at home Feb. 20, 1982--to the Eagles. Villanova leads the Big East at 9-2, with Georgetown at 7-3.

Martin Clark's rebound basket began BC's key 11-0 spurt to a seven-point advantage with 14:50 left. Murphy scored the last five points in the burst.

After St. John's drew to 68-63 with 7:06 remaining, John Garris hit a jumper and Murphy two free throws to boost the margin to nine.

Garris had 22 points and Michael Adams 15 plus six assists for BC. Chris Mullin led the Redmen with 21 points; Billy Goodwin had 19.