"It is too early to predict the outcome of these dramatic developments," Rasmussen told a Brussels news conference. "But coupled with the economic crisis, this could have a profound impact on us in Europe."
Rasmussen said NATO needs a new approach, something he termed "Smart Defense."
NATO must help nations to build greater security with fewer resources, but greater cooperation, coordination, coherence and flexibility, he said Monday.
Rasmussen said he sees pooling and sharing of resources, setting the right priorities and forging closer ties with industry as the way ahead.
Speaking about another matter, he said the price tag for NATO's new mega-headquarters in Brussels is expected to reach $1.4 billion.
"The final figure happens to be a bit lower than the original expectation" due to a drop in construction prices resulting from the economic crisis, Rasmussen said.
NATO's new headquarters are designed to replace a barrack-style compound that Belgium loaned the alliance in 1967 after it was kicked out of France.