San Francisco-NBC Internet Inc., the Web unit of the National Broadcasting Co., said it will cut its work force by 30 percent, or 150 jobs, because of a revenue shortfall stemming from a softening ad market. The cuts come less than six months after NBCi cut 170 jobs. The company cuts its revenue forecast for 2001 to $100 million from an earlier projection of $150 million. It reiterated that it expects to become profitable by the first quarter of 2002 if not the fourth quarter of 2001, before charges and promotion. NBCi's stock has practically dried up, going from a 52-week high of $106 down to trading around $4 per share last week.