WASHINGTON — Sen. Hillary Rodham Clinton cut into Sen. Barack Obama's delegate lead in early returns from Pennsylvania's Democratic primary.

Clinton won at least 52 delegates to the party's national convention, with 60 still to be awarded. Obama won at least 46, according to an analysis of election returns by The Associated Press.

The final delegate count isn't expected until Wednesday at the earliest because many of Pennsylvania's counties are split into multiple congressional districts. Pennsylvania awards delegates according to the statewide vote as well as the vote in individual congressional districts.

Election officials were working late Tuesday to assign votes from split counties to the appropriate congressional districts.

In the overall race for the nomination, Obama led with 1,694.5 delegates, including separately chosen party and elected officials known as superdelegates. Clinton had 1,561.5 delegates, according to the AP tally.

It will take 2,025 delegates to secure the Democratic nomination.

On the Republican side, Sen. John McCain clinched the party nomination in March.

The AP tracks the delegate races by calculating the number of national convention delegates won by candidates in each presidential primary or caucus, based on state and national party rules, and by interviewing unpledged delegates to obtain their preferences.

Most primaries and some caucuses are binding, meaning delegates won by the candidates are pledged to support that candidate at the national conventions this summer.

Political parties in some states, however, use multistep procedures to award national delegates. Typically, such states use local caucuses to elect delegates to state or congressional district conventions, where national delegates are selected. In these states, the AP uses the results from local caucuses to calculate the number of national delegates each candidate will win, if the candidate's level of support at the caucus doesn't change.