Engine 929 rested on its rails, humming patiently on Union Station's Track No. 12 as luggage-less passengers hurried down the quay to board one of three silver passenger cars bound for Baltimore.

Inside, whole families of Orioles fans in trademark hats and orange baseball shirts talked of batting averages and RBIs, of Cal Ripkin and Brady Anderson, of division standings and elusive pennant races. Children bounced along wearing their mitts, dreaming of catching a fly ball souvenir for the day.

The 80 or so passengers were cashing in on an experimental rail and shuttle-bus special to Memorial Stadium started this spring by the Maryland State Railroad Administration. Called "MARC to the Park," the train from Union Station takes fans to and from select Sunday afternoon Orioles home games.

Mark Dials, who works at the Union Station information desk, said he had been taking the $10 Eyre bus from the Orioles Store at Farragut Square NW, a two-hour ride each way, "but it's always so crowded."

"This beats driving any day," said Ron Kananen, of Great Falls, who was taking a friend's 6-year-old son, Skipper, to his first game and on his first train ride. "We love baseball, and this really makes it easy."

Round-trip tickets are $9 for adults and $5 for children. That includes a bus from Penn Station to the stadium and back. The train leaves Union Station at 11:30 a.m. and stops at New Carrollton, Seabrook, Bowie State, Odenton and BWI.

Tickets can be purchased at the station or on the train. The trip takes about 90 minutes each way.

"I took my kid to a ballgame earlier this summer and it took almost double the time with traffic," said David Spohn, of Northwest Washington, who was finishing up a morning bagel on the train.

Fred Wengenroth, an operations manager for passenger services for the State Railroad Administration in Maryland, said he and a group of co-workers came up with the train service idea.

"They had a train long ago that took fans to the stadium, but never recently," said Wengenroth. "This is our experimental year -- a dry run for when we expand service to the new stadium."

That stadium, which will open in 1992, will be near Baltimore's Inner Harbor and will be even easier to reach by rail: The train's final destination -- Camden Street Station -- is within walking distance of the stadium site.

"There won't be anything closer to the stadium than that station, except for maybe the hot dog stand," Wengenroth said.

"We like to say, 'Take the O's train,' " said Rick Vaughn, public relations director for the Orioles.

Sitting side by side, Scott Malczewski and friend Neal Halbran, both 8 and sporting baseball caps, could hardly wait to get to the game. "We want to catch a ball," said Scott.

"If this works out, we'll do this all the time," said his dad, Bill.

"MARC to the Park" has three more runs this season, Sunday and Aug. 19 and 26.