Battle for 2000 Senate starts early.(Knight Ridder Newspapers)

Consider these political questions:

Why are squads of U.S. senators parachuting into the Silicon Valley for lavish fund-raising events?

Why are Senate wannabes in New Jersey and New York airing ads that boast about their bona fides?

Why is Minnesota's freshman senator squirming over reports that local cops may have gone too easy on his son when they found him with marijuana?

Why has a Missouri Republican senator unearthed a photo of the state's Democratic governor performing in blackface at a 1960 minstrel show?

Because the battle for control of the U.S. Senate, which won't be decided until voters render their verdict in November 2000, has already moved into the bloodletting phase.

The Democrats lost the chamber in the conservative revolution of 1994 and are hungry for redemption. A Democratic majority would also signal major shifts in policy _ elevating issues such as gun control and health-care reform _ and in personnel. For one thing, Delaware's Joseph R. Biden Jr. would replace North Carolina's Jesse Helms as chairman of the Foreign Relations Committee.

On paper, the Republican majority _ 55 of the 100 Senate seats _ would seem to be impregnable. For the Democrats to gain six seats and seize control, they must knock off five Republican …