WE WERE GATHERED IN A PARKING LOT at the George Howard Building in Ellicott City comparing notes on how many years it had been since we'd ridden in a school bus -- years? Decades. This was to be a new historic tour in the roster run by the Howard County Department of Recreation & Parks, and we didn't know where we were going and weren't sure we should be guinea pigs.

When the bus arrived we smiled. It was new and shining and, we discovered, immaculate inside. The driver, smiling and formal, helped us aboard and went around adjusting windows for the warm day. We knew he was Mr. Mullinix and we also knew, cheery though he seemed, we wouldn't even think of asking his first name, even though our guide introduced herself only as Joetta.

We set out along Old Frederick Road and Mr. Mullinix mentioned that there were lots of Old Frederick Roads as well as Old Annapolis Roads, since almost every settlement had roads going to those towns. We slowed as we passed Dorsey Hall, presiding over a remnant of Old Columbia Pike, now supplanted by the divided highway U.S. 29. The hall was built in the 1770s and you can still see the remains of the old grist mill, which was standard equipment at every farm in those days. Mr. Mullinix mentioned in passing that Columbia Pike was once a stone-packed highway of the same granite used to build most of the old houses.

Then he swung into the development of Columbia Hills off 29 and past Dower House, built in 1772 by a Dr. Pue who married Mary Dorsey. It was also called Bethesda, Mr. Mullinix added, which meant healer in Hebrew. Its barn is now a church.

On to Oakland Manor, the oldest building in Columbia and owned by the development. It was used as the campus of Antioch College in Columbia until the new campus was built. Alighting from the bus, we picnicked near Oakland Manor's outbuildings.

Then, down Waterloo Road to U.S. 1, as old as any in Maryland -- the main stagecoach route in colonial times -- where once stood Spurrier's Tavern. Legend has it that Lafayette was due to stay there on a visit to America long after the Revolution, but went on when he learned of the road named Waterloo.

Joetta said that if we went south on Route 1, we'd get to Savage which, like Ellicott City and Elkridge, which we were heading for, has an industrial history. Its textile mills on the Middle Patuxent are being restored as museums. But Mr. Mullinix said we'd have problems with bridge weight allowance if we tried to go there. We'd already had to detour because of another bridge.

Before it silted up, the Middle Patuxent was navigable up almost to where I-95 crosses it. In bare-branch winter you can see the Commodore Joshua Barney House there, with its widow's walk on the roof. The commodore apparently could walk to work and his ships. Mr Mullinix added that nearby Guilford was a freed blacks community dating back to the early 1800s.

We passed Belmont built by Caleb Dorsey in the early 1700s, and now owned by the American Chemical Society which rents it out for conferences.

Next stop was Christ Episcopal Church, founded in 1711 and the oldest continuing congregation in the county. The present building, called "Old Brick," dates to 1809. The Dorseys donated the land when they got tired of going all the way to Annapolis to worship. It had itinerant preachers until "Athol," the pastor's house, was built in the 1730s.

The church was founded as Church of England and the pastor fled to England during the Revolutionary War. It was inactive until 1809 when it became Episcopal, Joetta said. She pointed out the separate doors for men and women. Yet blacks and white worshipped there together.

Not many old graves, someone observed. Mr. Mullinix pointed out that most people then were buried on their own property.

On toward Elkridge we went. It began as a summer home community of judges and lawyers from Baltimore in the early 1800s. Most of those original homes remain on Lawyers Hill Road, long since winterized, most enlarged. The Elkridge area was staunchly pro-South before and during the Civil War and there's a replica of the steam gun built there for the Confederacy to defend Harpers Ferry but, alas for the South, intercepted by Yankee sympathizers.

The Elkridge Assembly Room on Lawyers Hill Road was built to bring the divided town together after the war, Mr. Mullinix said.

We turned off to Elkridge Landing, which was a shipping point for tobacco in the 1600s. There was no bridge across the Patapsco then -- ferry barges were pulled by horses and probably by slaves.

Caleb Dorsey built a furnace there, probably in the 1600s, to refine iron ore from nearby Hanover. By the 1870s its successor was the Great Falls Iron Co., the biggest producer in the region.

Mr. Mullinix pointed out the profusion of willow trees where Deep Run fed into the Patapsco. People used to harvest shoots and sapling for baskets there.

Just upstream is the Thomas Viaduct, built in 1835 so the B&O could extend to Washington. It was named for the first president of the railroad and miraculously survived the three great floods of 1868, 1972 and 1975.

We crossed the river into Baltimore County, through Oella to Ellicott City, where we perched on the edge of a precipice looking down at the rock-strewn Patapsco. At some points there wasn't even a guard rail. Mr. Mullinix seemed oblivious. As we pulled into Ellicott City a train went along the tracks clinging to the hillside. It seemed it must tumble over.

Then we were back at where we had set out that morning. As Mr. Mullinix gravely helped us out, we each thanked him. He smiled just a trace and said, "Come again." HISTORICAL TOURS

The Howard County Department of Recreation & Parks runs many tours of historic county areas and homes, and is adding new ones as they are researched and tested and guides are trained. On some tours old homes are opened. Most are free; sometimes you have to pay for lunch. Also, seasonal tours for flowers and foliage. To sign up or to get on the mailing list for brochures, call 301/992-2485.