THEY DID IT LIFE IN THE BIG CITY

TALLEST BUILDING TOPPED OFF: As a lofty crowd of 200 engineers, architects and politicians looked on, the final girder was hoisted into place atop the city's tallest building, downtown's 73-story Library Tower. The $350-million skyscraper on 5th Street is part of a billion-dollar project which is to include a 54-story sister tower and the renovation and expansion of the city's Central Library. LONGEST CRIMINAL TRIAL IN RECORDED HISTORY: Entering its seventh calendar year and having cost taxpayers more than $15 million, the McMartin preschool molestation case may finally reach a conclusion in 1990. The 12-member jury left for vacation in late December after delivering 26 sealed verdicts. The jurors are due to return in January to rule on 39 additional counts, at which time the verdicts will be announced. LARGEST DRUG BUST IN HISTORY: Breaking open a $6 padlock, authorities entered a San Fernando Valley warehouse and discovered 20 tons of cocaine worth up to $6 billion on the streets. The cocaine cache, which federal officials estimated as 5% of the world's annual production, was stacked eight feet tall amid bric-a-brac that included plastic owls, plaster figurines,pinatas and a painting of Christ walking on water. MOST AREA CODES FOR ONE CITY: A mere five years after the introduction of the 818 area code in the San Fernando and San Gabriel valleys, phone company officials announced that the 213 area code will be subdivided again in 1992, making Los Angeles the only city to be served by three area codes. The new 310 area code will cover a U-shaped district stretching from the Westside to Long Beach to Whittier.