The New York Giants moved within a game of their first Super Bowl appearance ever by demolishing the San Francisco 49ers, 49-3, yesterday as Phil Simms passed for four touchdowns, Joe Morris ran for 159 yards and linebacker Carl Banks led a defense that shut down one of the NFL's top offenses.

Except for the first three minutes, when San Francisco's Jerry Rice fumbled away a sure touchdown, the Giants were totally dominant, winning their 15th game in 17 starts and 10th straight to move into the NFC title game here against Washington next Sunday.

The 46-point victory margin was the largest in an NFL playoff game since the merger of the NFL and American Football League in 1970. The most lopsided game before this was Washington's 51-7 victory over the Los Angeles Rams in 1983.

The Giants rolled to a 28-3 half-time lead with two touchdowns in the final 50 seconds, then scored three more in the third quarter. In the second half, San Francisco was forced to go with quarterback Jeff Kemp instead of regular QB Joe Montana. Montana left with a concussion when Jim Burt ran into him just before the half. On the play, Lawrence Taylor picked off a pass and returned it 34 yards for a touchdown.

Morris, held to just 14 yards on 13 carries when the Giants beat the 49ers 21-17 in San Francisco last month, carried 24 times for his 159 yards, including a 45-yd. TD scamper midway through the second period and a 2-yd. TD run in the third.