A city angling for conventioneers is busy adding rooms for them

For 11 years, from 1968 to 1979 not a single new hotel room was built in San Antonio. "People just didn't know anything about San Antonio," a businessman said.

Now, apparently, a lot more people do know about it The city is in the midst of a hotel-building and renovation boom that added more than 900 rooms last year , bringing its total to over 5,000.Construction under way and projects on the drawing boards could add more than 1,700 additional rooms in the next few years. Most of these are the direct result of an aggressive effort to attract tourist and convention business.

A note of caution, however, comes from those who feel the city needs more than conventioneers and tourists to support all these new rooms.

"San Antonio realy needs more office space and businesses downtown," says David A. Berins, a principal in the Houston office of Harris, Kerr & Forster & Co. The accounting and management firm is working on a study of the city's hotel needs for the San Antonio Convention and Visitors Bureau. The preliminary findings are expected early in October, Mr. Berins said.

Many of the businesses that are moving to San Antonio or expanding here are locating on the Interstate highway loop that circles the city, particularly north of town, near the airport. Unless it can persuade more companies to locate downtown, the city could find itself "overbuilt" in hotels rooms, he added.

Another study, nnothing that it costs about $90,000 a room to build a first-class hotel, argued that such a facility should have about a 75 percent occupancy rate to justify the costs. Occupancy rates near the airport were more than 85 percent this summer, while downtown the rate stood at just over 70 percent.

But Patrick Ziarnik, a convention bureau official, holds that while San Antonio should and will be able to attract new businesses downtown, it also has a big future as a convention city.

"By 1985, San Antonio will be the hottest convention destination in the Southwest," he says flatly.

The city's newest hotel, still under construction, will be a 637-room Hyatt Regency, which will be connected to an extension of the Riverwalk. It is expected to ope in mid-1981.

Other hotels that have been completed or expanded include a 502-room Marriott , a 250-room Four Seasons Plaza Nacional, and the Mansion del Rio, which added 173 rooms last year.

In addition, several older hotels, incluing the hilton, St. Anthony, Menger, Gunter, and the Crockett, have completed, begun, or announced major renovations since 1979.