This is what could end stock bull market: Paulsen

Bull markets end with bangs not whimpers: Blitzer
Bull markets end with bangs not whimpers: Blitzer

Stock valuations are "not excessive," but they're "not cheap" either, Wells Capital's James Paulsen told CNBC on Monday.

"If we're trading in the vicinity of 17½, 18 times, I think bull markets could end in the low 20s in terms of multiples," he warned in a "Squawk Box" interview.

Paulsen provided his take on price-to-earnings multiples when asked about warnings from closely watched hedge fund manager Seth Klarman about "nosebleed valuations." In a letter to clients of his $27 billion Baupost Group, Klarman also said there's potential for a brutal correction across financial markets.

(Read more: Klarman warns ofimpending asset price bubble)

Also on "Squawk Box," S&P 500 Index Committee Chairman David Blitzer said valuations are not at alarming levels yet. But he views them at "a bit more expensive" than Paulsen.

(Read more: Warning signs? Margin debt soars again)

"I think that bull markets end with bangs, not whimpers," Blitzer continued. "So I don't think it's going to creep up 19 [or] 20 times and fade away."

"Something will happen. And it'll blow it up at that point," he added, but said investors shouldn't worry too much about the situation in Ukraine unless there's military action.

Sunday marked the fifth anniversary of the bear market closing low following the 2008 financial crisis. The gains since then were 151 percent for the Dow Jones Industrial Average, 178 percent for the and 242 percent for the Nasdaq Composite.

For his part, Paulsen reiiterated his outlook in recent interviews—saying that stocks could level out this year with increasing earnings.

By CNBC's Matthew J. Belvedere. Follow him on Twitter @Matt_SquawkCNBC.