Like many parts of the Sun Belt, Arizona uncovers new traffic problems faster than the solutions can be found. The existing freeway system is inadequate, and Phoenix streets are burdened with increasingly heavy traffic loads.

Now, despite its well-deserved reputation for clear views, sunny skies and flat streets, Arizona finds itself becoming notorious in another area: its cities' streets have become the deadliest places to drive in the United States, according to 1980 statistics recently released by the National Highway Traffic Safety Administration.

More than 40 percent of the state's traffic fatalities occurred on metropolitan streets--the highest percentage of any state in the country. California was second with 36.9 percent. By way of comparison, in the District of Columbia 12.2 percent of fatalities occurred on local roads. The survey monitored 1980 traffic deaths on interstate highways, other federal roads, state routes, county roads and local streets.

Despite an 8 percent drop in overall traffic fatalities in Arizona--down from 1,029 in 1979 to 947 in 1980, the state scored poorly in fatalities recorded per 100 million vehicle miles traveled. It tied for fifth with Montana at 5.0 deaths, behind Nevada, 5.7; New Mexico, 5.4; Louisiana, 5.3; and Wyoming, 5.1.

Arizona transportation officials, like others in the West, blame an inadequate urban freeway system that forces a deadly mix of traffic--trucks, cars, motorcycles and even mopeds--onto increasingly congested city streets.

"It's a rural interstate system," said Roger Herzog, transportation planning officer for the Maricopa Association of Governments, a regional planning body. "In the beginning stages of the interstate program, let's face it, Phoenix and Arizona were pretty much rural-type areas. The big problem was connecting cities a long way apart . . .we've focused on rural, intercity links."

Local officials also say that because the skies are almost always clear, drivers are unfamiliar with the driving techniques needed when rain and dust storms come. Expansive streets also tempt drivers to speed, they say.

Another complication was that Phoenix voters kept shifting their view on an urban freeway system, fearing construction of the roadways would turn Phoenix into a Los Angeles. So by the time a freeway plan was approved, federal funds had dried up. "Now we're coming in kind of at the end of the major interstate [construction] era, trying to finish up the urban link we have here," Herzog said.

State and city officials are developing a five-year, $110 million freeway and highway construction plan using funds to be generated by upcoming increases in the state gasoline tax. They also bank on congressional approval of a $5 billion proposed federal increase in gasoline and trucking taxes, because Arizona officials believe that will improve chances the federal government will start construction of an $869 million Phoenix freeway called the Papago. Arizonans have debated the merits of the road for nearly two decades, and current plans call for its completion by 1990.

Federal officials aren't convinced, however, that an inner-city freeway system will end the traffic carnage on Arizona's city streets.

A recent study conducted by the National Highway Traffic Safety Administration found that nationally, 50 percent of traffic fatalities were alcohol-related, said Robert Ross, a spokesman for the agency. "The causes of fatalities are speeding, drunk driving and also lack of enforcement. When you're riding around suburbia, you're in a greater risk than on the interstate highways. Drunks aren't on the interstate system. They're trying to get home."