Speaking to Italian daily La Repubblica, Stoltenberg said: "Nato is ready to help Libya construct its security institutions".
Nato experts were already "in contact with Libya authorities to see how to assist them better," he added.
"Any support from Italy would be welcome but that is up to the Italian government," he said.
Libya has been gripped by chaos since a Nato-backed uprising toppled and killed dictator Moamer Kadhafi in 2011, with rival administrations and multiple militias vying for control of the oil-rich country.
The chaos has seen the country become a key departure point for thousands of migrants hoping to reach Europe, with hundreds drowning each year trying to cross the Mediterranean. Hundreds and thousands of migrants making the perilous journey have arrived in Italy in recent years.
Italy's new populist government has vowed to curb arrivals, banning foreign NGO rescue ships from their ports and appealing to Nato for greater help tackling illegal immigration and human trafficking.
"There are no military solutions to the migrant crisis, but Nato will help to make the problem less serious," said Stoltenberg, adding that Nato deployments in the Aegean Sea "have helped to suppress illegal and dangerous trafficking of human beings."
He said Nato would sign a joint declaration with EU President Donald Tusk and EU Commission chief Jean-Claude Juncker to outline their cooperation.
Italy's new government has affirmed its commitment to the alliance despite differences in political policy. Italy advocates a review of economic sanctions against Russia which Nato believes are necessary. But Stoltenberg said Italy remained an important member.
"I expect to continue working with Italian Prime Minister Giuseppe Conte and his government," he said. "Italy has a fundamental role in the future of Nato."