BALTIMORE, JULY 20 -- On schedule and $20 million under budget, this city's fledgling Metro train system opened a second leg of its 14-mile rail line to paying passengers today, linking Baltimore's downtown business core with the rapidly growing suburbs northwest of the city.

Despite some predictable confusion among passengers about fares and schedules, Metro officials pronounced opening day a success.

"Everything's working fine," said Metro spokeswoman Anita Pesses. " . . . I think it looks pretty good."

The six-mile, $177 million addition creates three stations in suburban Baltimore County and connects with the original eight-mile segment of track opened in the city more than three years ago at a cost of $1 billion.

A third, 1.5-mile segment between the downtown central business district and Johns Hopkins Hospital in East Baltimore is being designed and is slated for completion in the early 1990s at a cost of $300 million.

Baltimore's single 14-mile rail line with 12 stations -- minuscule compared with Washington Metro's older 69.6-mile network of interconnecting lines and 60 stations -- carries about 45,000 passengers a day. Pesses said Baltimore Metro hopes to pick up an additional 7,500 to 10,000 passengers initially with the new segment and even more in the future as bus lines are realigned to feed into the rail system and new commuters learn of its availability.

Average daily ridership on Washington's Metro is near a half-million.

Baltimore's Metro line runs in an almost straight path northwest from the center of the city through predominantly middle- and working-class black neighborhoods of west Baltimore into the sprawling, largely white residential developments outside the Baltimore Beltway.

It terminates at Owings Mills, where a massive shopping mall opened last year. A spur of the Baltimore Beltway, I-795, feeds car traffic into the shopping mall. Mall shop owners now hope that Metro's new rail line, which runs down the median strip of I-795, will not only help suburban commuters go into the city but also will lure city shoppers out to Owings Mills.

Passengers interviewed on the trains today generally gave the newly opened segment of Metro high marks.

"It's easier, more convenient, quicker," said Marsha Palmer, a downtown Hecht Co. sales clerk who was taking the day off to shop in Owings Mills. Until today, if she wanted to go there from her west Baltimore home, she had to get off Metro at Reisterstown Plaza, the old terminus, and take a 30-minute bus ride the rest of the way. Now she can take the train all the way in half the time.

Ruth Bradford, a Baltimore County resident who commutes to her job at the Maryland Department of Health and Mental Hygiene in Baltimore, was trying the new leg of the train system and said she liked it.

"It will save me time, but I don't know if it will save me money," she said. Until today, she drove from her home in suburban Hamsted to the old Reisterstown Plaza terminal and parked in the Metro lot free, if there was a parking space left at the crowded station. Now she can drive to the much-closer Owings Mills station and still park free in a much bigger lot with plenty of extra spaces.

"I just don't know yet if the bigger fare I pay {on Metro} is more than the gas I use driving all the way to Reisterstown Plaza," she said.