(Bloomberg News) JPMorgan Chase & Co. Chief Executive Officer Jamie Dimon and Goldman Sachs Group Inc. CEO Lloyd C. Blankfein predict Wall Street will rebound from 2011's trading-revenue plunge. Rivals and analysts aren't so sure.

Fourth-quarter earnings reported by the six largest U.S. banks show the industry suffered a third straight quarterly drop in combined trading and investment-banking revenue. On conference calls this week, analysts are pressing executives with a similar refrain: Is it a temporary rut or a lasting shift to smaller volumes, profits and pay?

"This is a big debate," said Paul Miller, a former examiner for the Federal Reserve Bank of Philadelphia and an analyst at FBR Capital Markets in Arlington, Virginia. "A lot of bears are saying it is due to regulation and deleveraging, and some are saying it is cyclical. I think it's some of both."

Executives and analysts are focusing on whether stiffer regulations, capital rules and a weak economy may solidify a decline in revenue after the European debt crisis curbed trading volume and corporate dealmaking in last year's second half. Credit Suisse Group AG, UBS AG and Royal Bank of Scotland Group Plc, which are all shrinking their investment banks, have announced plans to eliminate about 8,300 jobs since the start of November.

'Snap Back'

"We'd all hoped that the headwinds to our business, including low levels of client activity, low interest rates, market volatility and political uncertainty around the world would subside," Credit Suisse CEO Brady Dougan told analysts Nov. 1. The bank said that day it would cut about 1,500 jobs, in addition to 2,000 previously announced, and reorganize its securities unit after reporting third-quarter profit that missed analysts' estimates. "It's now clear, however, that these secular trends may persist for an extended period," he said.

Dimon and Blankfein have since sought to reassure investors that markets and earnings from securities units will rebound.

"The world will snap back, and it will be a surprise, and it will be faster than people think," Blankfein, 57, said at a Nov. 15 investor conference. Yesterday, Chief Financial Officer David Viniar echoed the remarks after the firm said trading revenue fell 25 percent from the third quarter to $3.06 billion.

"We are clearly in a cyclical downturn," rather than a secular decline, Viniar said. "There is less activity that is cyclical. That will come back. I have no idea when, but it will come back."

Dimon, 55, said investment banking is a volatile business in which volumes can swing by 50 percent daily.

'Boom Again'

"It's not a mystical thing," he told reporters on a Jan. 13 conference call. "You just have to manage the business carefully and understand it's going to have those kinds of swings. I don't think the lower numbers are permanent. I think when things come back, these numbers will boom again."