The Century Freeway in Los Angeles is one of 25 unbuilt urban freeways on the interstate highway system that are listed as "controversial" by the Federal Highway Administration. The states are under enormous pressure to resolve those controversies or lose billions of federal dollars.

Federal law gives the states only until Sept. 30, 1983, to decide once and for all to build the controversial sections or to transfer the money for those sections to other highway or to transit projects. More than $2 billion in such transfer funds has been used for the Washington subway, for example, as well as for projects in Boston, Portland and other cities.

If the deadline is not met, the uncompleted sections or the federal money that could have been transferred will be dropped from the books. Once states decide to build an interstate freeway, they must have it under construction or under contract by Sept. 30, 1986, or lose federal funds at that time. Federal funds pick up 90 percent of the cost of interstate construction.

The Federal Highway Administration's list-of controversial segments totals 330 miles projected to cost $6.7 billion. Of those segments, states have indicated varying degrees of interest in transferring about $5 billion (and 230 miles) to other highway or transit programs. That would leave 250 miles of urban freeways still to be constructed, including 150 that are not regarded as controversial.

By far the most controversial uncompleted interstate link is the Westway project in New York City (I-478). It is only 4.2 miles long and carries a $1 billion price tag, making it potentially the most expensive transportation project per foot in history.

Westway would replace the collapsed West Side Highway, and would include repair work on the cross Hudson River transit tubes. The project has been the subject of years of turmoil involving federal, state and local officials and has occasionally found the Environmental Protection Agency and the Federal Highway Administration speaking with different voices.

Eleven of the 25 controversial segments are in litigation, including supposedly approved projects such as the Mercer Island freeway in Seattle (I-90). That project (7.5 miles at $679 million) would eliminate a marvelous (but dangerous) S-curve in the middle of the bridge across Lake Washington. That is the major commuter artery between Seattle and its eastern suburbs.

There are also major freeway controversies in Tucson, Hartford, Honolulu, Shreveport, Detroit, Philadelphia, Trenton, Dayton, Oklahoma City, Providence, Memphis, Richmond and Allentown, Pa.

In almost every case, opponents charge that completion of the freeway will just add traffic and gasoline consumption to an already degraded area, plus abet flight from cities to suburbs. Historic or architectural preservation arguments are used in some cases. Proponents inevitably counter with the economic benefits massive public works projects bring, including jobs for construction workers and highspeed access for truck-dependent industry.