"The West Wing" team won the Emmy for outstanding drama series in 2001

Sorkin has written most of the West Wing episodes since the series bowed in 1999 and also served as executive producer. Another executive producer, Thomas Schlamme, also is leaving the series.

"This has been the experience of any writer's dreams," Sorkin said in a statement. "I had the best job in show business for four years and I'll never forget that."

In the statement, Sorkin and Schlamme said they plan to pursue other film, television and theater projects.

The move comes as The West Wing, now in its fourth season, saw a dramatic dip in ratings in its 9 p.m. Wednesday slot against ABC's The Bachelor and Fox's American Idol. According to The Associated Press, there had been reports of tension between Sorkin and Warner Bros. Television and the studio had reportedly cautioned him about budgets and production delays.

Sorkin has won an Emmy for writing for the series, which won its third consecutive best drama trophy at last year's Emmy Awards. Schlamme has won two Emmys for directing.

The show will continue under executive producer John Wells, whose other series include NBC's ER and Third Watch. He said a team of writers, directors and producers has been assembled to help in the transition.

"Aaron Sorkin and Tommy Schlamme are irreplaceable," Wells said in a statement. "They will be sorely missed."