PARIS — France and Italy said Wednesday that they would join Britain in sending liaison officers to support the rebel army in Libya, in what military analysts said was a sign that there would be no quick and easy end to the war in Libya.

The dispatching of the liaison officers — probably fewer than 40 of them, and carefully not designated as military trainers — is a sign also, they said, that only a combination of military pressure from the sky, economic pressure on the government and a better-organized and coordinated rebel force will finally convince Col. Muammar el-Qaddafi that he has no option but to quit.

“Some countries thought the Libya operation could be over quickly,” said a senior NATO ambassador. “But no military commander thinks so.”

Sending advisers to Libya is the latest in a series of signs of trouble for the NATO campaign, which began in earnest with a stinging, American-led attack but has seemed to fizzle since operational command was transferred to NATO on March 31. After that, a rebel offensive was smashed by Colonel Qaddafi’s forces, which sent the rebels reeling toward the eastern city of Ajdabiya.