Amy Crews-Cutts, senior vice president and chief economist of Equifax, said auto finance companies have ramped up the number of leases they are providing to well-qualified borrowers with higher credit scores. In California, Florida and the Northeastern part of the country, leases are especially growing in popularity, she added.

Finance companies have a 10% capture rate on lease financing among all U.S. auto lenders, according to Equifax and CreditForecast.com. Lease balances increased by 11% in March from a year ago. Through the end of 2017, they are expected to grow at an 8% average annual rate. Meanwhile, auto loan balances are set to increase between 2% and 3% annually during the same period.

 CUNA said new auto loans represented 10.1% of credit union loan portfolios as of March. The percentage was down slightly from 10.8% in March 2011. Used auto loans grew from 18% last March to 18.7% in March of this year.

Following a first-quarter sales boom, vehicle sales held steady during April, said David Carrier, NAFCU chief economist and director of research.

"The mild winter months likely captured some sales from the spring, and the fact that sales figures did not deteriorate in April reflects the strength of pent-up demand in the market," Carrier said. "The mix of purchases has been heavily swayed by gas prices."

As fuel prices climbed steadily during the winter, buyers focused on fuel-efficient cars, Carrier pointed out. Now that prices at the pump have moderated, he said the mix is shifting back toward trucks and SUVs.

"Credit conditions are easing, and subprime lending activity is on the rise. Barring a setback in the labor market, vehicle sales should keep its strong pace throughout 2012," Carrier said.

The 1.9% gain in vehicle loans is a significant reversal of trend from the 4.1% decline at this time last year, according to Dave Colby, chief economist at CUNA Mutual Group. New vehicle loans were off $3 billion, while used vehicle loan growth accounted for 51% of the annual change in lending.

While vehicle loans remain a strong slice on credit union portfolios, Colby said another type of loan may be a prominent factor toward sustaining loan growth.

"With some portfolio components showing growth rate improvements and a reduced rate of contraction in others, we are forecasting annual growth of 4.1% in 2012 for the total loan portfolio," Colby said. "This is a big improvement from the 0.4% average annual gain of the past three years but well below long-term trends and what is needed to sustain capital growth via spread income."