Just a crab's throw from the inner harbor shores where Maryland mariners moored their boats, another anchor of sorts is nearing completion - Baltimore's convention center.

So you didn't know Baltimore had a convention center? Then, you probably didn't know that the bay city's downtown redevelopment is growing like hot (crab) cakes, partly from expectations of the convention center holding everything in place.

The center, scheduled to open next month, will compete for business with Washington, New York, Philadelphia and Boston. Ironically, Baltimore's boosters boast that not only does the city now have its own amenities to compete with neighboring Washington, but conventioneers will be lured to Baltimore with Washington as the bait.

"Baltimore is going to become one of the major convention cities on the Norteast coast," said James Smither, one of the people in charge of hooking and reeling in would-be conventioneers. Such dogma a decade ago would have been considered a joke. "People are totally surprised by what Baltimore has to offer. It's the biggest secret on the East Coast."

Smither said that the he expects "no competition" from Washington's $99 million convention center, scheduled for groundbreaking next January. "Suddenly there's another city they can come to. They probably don't expect to see what will become the most beautiful convention center in the country. It's not the biggest, but it's the best."

"We don't have the distraction of the major tourist draws," Smither said. Baltimore is cheaper, too, he added.

The concrete, steel and glass center is in the midst of more than $615 million in private urban renewal investment in the downtown area. Years ago, the city's inner harbor area was known more for its stench of rotting piers and fish rather than the aroma of outdoor cafes and shadows of skyscrapers in the area now.

Where dilapidated old factories mar one of the views from the convention center's outdoor terrace, a $170 million office-residential complex of condominiums, plazas and retail stores soon will be built.

Unlike Washington's convention center, which spawned protests from community residents who would be displ aced, Baltimore's center displaces nothing but old warehouses, relics of a bygone era, said Sherrie Hirsch, director of advertising and promotion for the convention center.

Still, there was controversy over the necessity of a convention center: Another waste of taxpayers' money, critics said. The center's cost originally was estimated at $45 million. Because of additional equipment costs, that figure rose to nearly $50 million, with the additional funds coming from the city, Hirsch said. One city official said most of the oppositon came from residents of Montgomery and Prince Georges counties who did not want the center located in Baltimore.

The center will be profitable within two years, Smither said. To make a profit, the building needs to bring in revenues of $2 million a year, and "for 1979 and 1980 we're almost at that figure already," Smither said. Revenue estimates are based on rental, electrical, plumbing, catering and some employe costs, Smither said.

The center has booked 20 national conventions, most through 1984, with total revenues of $20 million expected. Sales taxes accruing to the city from that amount would equal $1 million, Hirsch said.

But Smither added that $20 million spent by conventioneers "will turn over five to seven times before it leaves the city." Assuming those revenues turn over five times, Smither said, "With a 5 percent sales tax on $100 million, that's $5 million."

Smither said the center has sold out most of the space for the first half of September, all of October and November, all but six days of January and all of February, March, April and May. Some of those dates, however, are allotted to state and regional groups, which mean less outside revenue for the city.

"The average conventioneer spends $70 a day based on a 3.9-day stay," Hirsch said.

"They spend a tremendous amount of money, but we're not building roads for them, or any schools. We just get their money," Smither said.

The convention center has 115,000 square feet of unobstructed exhibit space that can be divided into four separate halls with expandable doors. The center, whose current rough concrete and dust will be replaced by polished floors and plants next month, also has 41,000 square feet of meeting room area in 26 rooms, some of which also have expandable walls.

The center will be connected by pedestrian walkways to the 500-room Hyatt Regency Hotel, which will be built across the street, and another connecter will link the center to the Chesapeake & Potomac Telephone Co. office, which also has a small retail center. Another bridge will connect the center to the Equitable Bank building, also under construction.

Plans are to replace the vacant ware-house not far away with another hotel, Hirsch said.

Until recently, Baltimore, like a number of other cities, didn't focus on convention business. Most of the city's conventions were held in the area's hotels or at the Baltimore Civic Center.

But the center has a capacity of only 13,000 persons. "If the meeting was for 10,000 persons, it would be perfect," Smither said of the civic center. "But for most meetings of 10,000 persons, you need meetings rooms."

The enormous revenues brought in by national groups make convention centers attractive. Chicago's sprawling 800,000 square feet of exhibit space in McCormick place, for example, grossed $8.4 million in one year with a profit of $714,000. But Baltimore isn't planning to attract groups that large, Smither said.

"What dictates the size (of the convention) is the number of hotels in a city," Smither said. "We didn't want to build a place the size of McCormick place. Chicago has the hotel space. We don't."

"This meeting facility can handle 85 percent of the meetings in the U.S. There are about 10,000 national meetings," he added. "Big cities are battling for them."

To prove their point, Smither and Hirsch noted that 3,000 members of the American Institute of Aeronautics and Astronautics will convene in Baltimore. It used to meet in Washington.

They said another major catch is the American Bowling Congress, which will set up 40 bowling lanes for 100 days in one of the center's exhibit halls for its national bowling tournament. Smither said "they'll be using 500 hotel rooms for 90 nights." CAPTION: Picture 1, Baltimore convention center under construction: expected to hold redevelopment in place; Picture 2, The center's interior: One hundred fifteen thousand square feet of unabstructed exhibit space. Photos by Douglas Chevalier - The Washington Post; Picture 3, Work proceeds on Baltimore's convention center: An expected $20 million will be spent there by conventioneers. By Douglas Chevalier - The Washington Post