Howlett, who turns 30 on Sunday, is in the second season of a three-year deal with leading Irish province Munster, giving him time to return home and become eligible for selection for the 2011 tournament in New Zealand.
"The experience with Munster has been wonderful so far," he told the Wales on Sunday newspaper.
"But there's a World Cup in 2011 in New Zealand which is a huge carrot for any rugby player.
"I will reassess closer to the time whether I feel I'm playing well enough to warrant a go at an All Blacks jersey.
"It's a World Cup and they don't come easily."
Howlett scored an All Blacks record 49 tries in 62 tests.