Continuity comic strips -- those adventure-soap opera features with extended storylines -- are losing readership and slowly dying out, according to Sarah Gillespie, managing editor/comics for United Feature Syndicate. Surveys by her syndicate show that the majority of continuity-strip readers are 50 and older. "They are adamant, enthusiastic readers, but there aren't that many of them."

(A recent Editor & Publisher survey of comic strips placed five continuity strips among the top 30, with "The Phantom" the most popular of them, in 20th place. The others: "Prince Valiant," 27th; "Mary Worth," 28th; "The Amazing Spider Man," 29th, and "Dick Tracy," 30th.)

"As the writers and artists who do those strips retire," she predicts, "you will see fewer and fewer such strips on the comics pages. Readers today want fewer words and 1-2-3 strips, a couple of panels to set it up and then the gag."

For example, the 52-year-old "Joe Palooka" continuity strip ended Nov. 24 after the retirement of artist Tony DiPreta. Appearing in 900 newspapers at one time, it was down to about 200 clients when it ceased publication.

On the other hand, "Blondie," which is not a continuity strip, is 54 years old and still going strong (1,990 clients and second only to "Peanuts").

"People are reluctant to commit themselves to continuity strips," says Kirk Nicewonger, promotion manager at United Feature. "They tend to prefer gag-a-day strips. I would guess people have less leisure time to do anything these days, including reading the comics pages."

Nicewonger says his syndicate receives "at least 10 new comic-strip offerings every day, more than 3,000 a year." The chances of being accepted by a syndicate? "Around 1 in 1,000. We launch about three to five new strips a year."

Occasionally a popular strip will die when its creator retires or dies; other times, it lives on. When Milton Caniff stopped doing "Terry & the Pirates" in 1947 after 13 years, George Wunder took it over and that feature continued for another 25 years.

"L'il Abner," however, which had 363 newspaper clients at the time, stopped running when creator Al Capp retired in 1977.