FACTBOX: Delegate counts for U.S. presidential candidates

(Reuters) - Delegates at national party conventions in August and September will be the key to selecting the Democratic and Republican candidates who will face off in the U.S. presidential election on November 4.

Voters choose the delegates state by state.

The field of candidates has narrowed and Sen. John McCain of Arizona has clinched the Republican race, while the Democratic contest remains close between Sen. Barack Obama of Illinois and Sen. Hillary Clinton of New York.

Here are the total numbers of delegates awarded so far in nominating contests to the leading candidates, as estimated by MSNBC. Other news organizations may have reached different estimates.

DEMOCRATS (number needed for nomination 2,025)

- Barack Obama 1,355

- Hillary Clinton 1,213

REPUBLICANS (number needed for nomination 1,191)

- John McCain 1,230