By Lynne Olver

TORONTO (Reuters) - First-quarter net profit grew 7 percent at Sun Life Financial (SLF.TO: Quote, Profile, Research), the insurer said on Tuesday, but global credit pressures and a robust Canadian dollar took a bigger bite out of operating earnings than analysts had expected and executives warned a tough year lies ahead.

Sun Life's stock skidded on the Toronto Stock Exchange, falling 4.4 percent to C$47.05 in morning trading.

Executives of Sun Life said during a conference call that difficult first-quarter economic conditions will hinder their goals of 10 percent growth in operating earnings per share, and 15 percent return on equity.

"At this point, we expect the balance of 2008 to remain challenging," Sun Life Chief Executive Don Stewart said.

A scenario of "little or no growth" could be a reality for 2008, Chief Financial Officer Rick McKenney said.

"An economic slowdown in North America, uncertainty in the capital markets and the strength of the Canadian dollar may limit short-term earnings growth, much like they did this quarter," McKenney said.

However, the company is taking steps to cut costs and re-prioritize projects, McKenney said.

"Specifically, we will reduce both our project costs and discretionary, general and administrative costs this year," McKenney said.