LOS ANGELES — IN desperation, some banks are posting warning signs that proclaim "Robbery Protected." Others give burglars "exploding money dye packs concealed in bills that are designed to blow up after thieves leave, staining them and the loot with incriminating ink.Full-page advertisements display mugs of robbers in the hope that someone can identify them - a 10 Most-Wanted List in the morning paper. Such are the tactics financial institutions are using to erase southern California's dubious distinction as the bank robbery capital of the world. While bank robberies are up nationwide, nowhere are they more in evidence than in the seven-county Los Angeles metropolitan area. Consider these Bonnie-and-Clyde statistics from the local office of the Federal Bureau of Investigation (FBI): * There have been 1,650 bank robberies in the region so far this year - an average of nine a day. That is the same as in all of 1990 and puts the area dejectedly on track to break the 1983 record of 1,830. * One in five bank robberies in the United States last year occurred here - more than in New York (520), San Francisco (532), Phoenix (226), Denver (77), and Dallas (78) combined. * In one six-day period in August, thieves hit more Los Angeles-area banks (67) than in Albany, N.Y., in all of 1990. "There really isn't a second place," says Ed Pistey, director of security for First Interstate Bank and chairman of the security committee for the California Bankers Association (CBA). The phenomenon says something about California as well as the nation. Bank robberies across the country have been rising for several years, though they jumped more than usual last year (17 percent). Some analysts say they believe the recession may have had a hand in that. As for local factors, Los Angeles has among the highest concentration of banks in the country, a product of the region's sprawling suburban profile. A web of freeways gives robbers easy escape routes and plenty of traffic to blend in with. Drugs - a motive behind so many robberies today - are the cause of a particularly large number here. The local office of the FBI, the lead agency in handling bank jobs, estimates 80 percent of the hits in the region are the result of someone trying to support a habit or under the influence of drugs. The area's relentless population growth and branches that are open more hours, including many on Saturday and even a few on Sunday, haven't helped keep the problem in check. "We're being stretched to the maximum right now," says John Hoos of the FBI office here. Bank robberies are not well-planned affairs by groups who know everything down to a teller's cologne. While organized rings exist, most are "acts of desperation" - spontaneous hits by individuals in need of money. Often, people do not go into a bank before burglarizing it. "It is very amateurish," says Jack Katz, a crime expert at the University of California, Los Angeles. Partly because of this, few robbers end up with a bungalow in the Bahamas. Authorities here catch 85 percent of the people who hit banks, though recovery of the loot is far less consistent. To try to stem the problem, banks are using a variety of tools in addition to alarms and the ubiquitous surveillance camera. The CBA has had some success in periodically taking out newspaper advertisements that feature photographs of alleged robbers. Many institutions do "trend analyses" to try to figure out why certain branches are hit so often. In studying one site in San Francisco, First Interstate found that burglars always used a side door. It made for convenient access to a getaway car and a freeway 60 seconds away. The bank locked the door and robberies at the branch have virtually ceased. As for gee-whiz innovations, such as tellers giving out loot with hidden transmitters so authorities can track criminals, security officials are mum on those for obvious reasons - though they do want robbers to know the lamp is on in the foiling room.