The big mystery for banks this earnings season is a whodunit: Which big lenders are behind a surprise yearend surge in lending?

Market watchers will dig deep into the results of two prime suspects that kick off reporting Friday — JPMorgan Chase & Co. and M&T Bank Corp. — for clues about which large banks are beneficiaries of a rebound in business lending indicated by federal data.

If borrowing is indeed coming back, swelling loan books — rare as spotted owls or Tarp-loving bankers — may join profitability and bailout-money-free balance sheets as the key markers of top-tier banks. Investor expectations for good news about new loans at JPMorgan Chase and M&T are high because they are among the few lenders lauded for largely doing things right through the crisis.

"Balance sheet growth will be one of the differentiators in 2011," said Jason Goldberg, an analyst at Barclays Capital who covers large and midsize banks. "If you see it, it is going to be modest. It will be mixed. Some banks will have it and some banks won't."

Weekly Federal Reserve data on loans and assets suggests that at least some of the country's 25 largest commercial banks saw improvement. Numbers released on Jan. 7 indicate big banks' loan balances nearly broke even during the last three months of the year after a two-quarter decline. Big banks had an uptick in commercial and industrial loans — or non-real-estate-related business lending like equipment or capital expenditure loans.

Last year's big question about banks involved the ending of loan losses, which have become less of a concern as the economy stabilizes. The federal data spurs a new one.

"Who can demonstrate loan growth?" asked Fred Cannon, co-director of research and chief equity strategist at Keefe, Bruyette & Woods Inc. "JPMorgan is the first one out so we'll be looking hard at them. … The main area we are going to be looking for is business lending."

Cannon's description of the fourth quarter: "It's a test for who can grow loans. … To the extent that you can, you'll probably do well throughout 2011."

JPMorgan Chase moved close to passing that test in the third quarter, reporting a quarter-over-quarter uptick in middle-market and commercial term lending at its commercial bank. Auto lending and mortgages were up, too, though companywide total loans contracted about 1.3%.

Analysts and investors are deeply curious to learn which way JPMorgan Chase's total loan balances moved, especially since a spike in merger activity breathed life into the long-dormant syndicated loan market, an area where JPMorgan Chase and other large banks were highly active before the downturn.

Jamie Dimon, JPMorgan Chase's chief executive, projected optimism about the health of his company and the economy at large on Tuesday, announcing the company's intention to raise its dividend in the second quarter.

"America will get its mojo back sooner rather than later," Dimon said in an interview on CNBC.

M&T, meanwhile, is JPMorgan Chase's financial peer in spirit, if not in practice. It's a regional bank; JPMorgan Chase is a global bank. But like JPMorgan Chase, M&T, which is based in Buffalo, N.Y., has been lauded for deft risk management and shrewd acquisitions through the crisis. Its total loans contracted in the third quarter, too, though it reported an increase in consumer real estate loans because it began to keep mortgages on its balance sheet rather than sell them to the housing agencies.

M&T executives have been frank about not trying to outpace the economy when it comes to loan growth, with its non-real-estate commercial loans contracting for at least four straight quarters.

A key question facing the company is whether it stuck to that philosophy in the fourth quarter as big rivals along the East Coast aggressively pursued new business clients.

Synovus Financial Corp., of Columbus, Ga., operates just outside of M&T's area of operations in the South.

It has been hiring more asset lending specialists and other business bankers as competition heats up for commercial and industrial borrowers, a group that almost every sizable bank in the country is interested in wooing at the moment.

"We are playing offense on C&I," Kessel D. Stelling, the president and CEO of Synovus, said on Monday. "It's a competitive landscape."

He said increasing loans is a challenge.

"Anecdotally we're seeing more activity. Our bankers are showing signs of optimism," he said. "I can't declare victory there. There seems to be a thawing out."

That sentiment is supported by the Fed's weekly H.8 filings, a sound if imperfect snapshot of bank lending activity.

Industrywide, total outstanding loans and leases at the 875 institutions surveyed by the Fed contracted for the third straight quarter.

Problem loan categories like commercial real estate continued to contract as banks run them off their books.

There was a typical holiday season surge in consumer-related borrowing. Mortgage lending was up modestly, too.

Though small banks continued losing loans, large institutions fared better, particularly in commercial lending. Loans and leases at the 25 biggest banks on Dec. 29 fell less than 1% from the prior quarter, to $3.931 trillion. C&I loans at big banks, meanwhile, were up 1.6% (or 6.6% at an annualized rate).

Those numbers, experts say, could be ominous for community banks.

"A lot of those small banks are really going to need to make a push into business lending," Cannon said.

"It is not a positive sign for the smaller banks."