A flurry in Folsom: apartment developers swarming. (California)

Apartments are suddenly so hot in Folsom that they could some day represent 20 percent of the city's total housing stock.

Developers are building or plan to build 4,134 apartments there, investing more than $280 million.

A Bay Area developer, meanwhile, has purchased the city's most prominent apartment complex for $28.7 million. The company, Interland Corp. of San Mateo, also plans to build. Between the two projects, Interland alone will spend $57 million.

Fifteen apartment complexes are in the works, including a 434-unit complex by Shasta Real Estate Co. that was approved last week. About half the apartments are already under construction or almost ready to be built.

And there's more to come. This year, the Folsom building department has issued permits for 564 units, up 300 percent from the 141 permits issued for all of last year. From 1991 to 1996, only four building permits were issued for apartments.

Opposition is mounting.

Last week, the Folsom Planning Commission turned down a proposal for a 260-unit …