SULTAN, Libya – Moammar Gadhafi’s warplanes bombed a military airport in Benghazi on Wednesday, the first assault on the eastern rebel stronghold since a revolt by inexperienced fighters with looted weapons began one month ago in an attempt to topple the Libyan strongman.

The airport attack came as government troops moved to tighten their grip on Ajdabiya, 95 miles south of Benghazi, while rebels armed with rocket-propelled grenades and traveling in speedboats fired on Libyan ships off the Mediterranean coast.

A succession of battles sent refugees fleeing as government soldiers pushed to crush the uprising. Gadhafi’s son scoffed at the threat of a Western-backed no-fly zone, and predicted that the fighting against an often erratic and confused insurgent force was about over.

A siege of Benghazi would test the tactics and tenacity of rebels who have often fled under heavy onslaughts by better-armed government troops. There are almost no defensive fortifications around Libya’s second-largest city, but opposition leaders say they would fight a guerrilla war, and Gadhafi lacks the soldiers and supply lines to triumph.

Separately, The New York Times reported that four of its journalists were missing in the region. It said it had received secondhand information that reporters Anthony Shadid and Stephen Farrell and photographers Tyler Hicks and Lynsey Addario had been picked up by government forces near Ajdabiya.

Government troops attacked Ajdabiya on Tuesday, holding it for hours before withdrawing to the outskirts as rebels launched a counteroffensive. By Wednesday morning, with warplanes circling high overhead and rebels racing down desert highways in pickup trucks, Gadhafi’s forces surged on the city again. Smoke plumes rose on the horizon and civilians gathered their belongings and fled.

“The shelling went on until 3 a.m.,” said Mari Atiya, who was escaping in a truck with his wife, two children, five sheep and cartons of diapers. “When it stopped, we saw people dead in the street and cars destroyed. There were snipers on rooftops with red lasers on their guns, and they shot teenage boys who raised their arms.”

Gadhafi’s son Seif Islam claimed in a television interview that the fighting was nearly over: “In 48 hours, everything will be finished.” He said it was too late to impose a no-fly zone.

In Benghazi, many residents remained defiant, but were also seemingly oblivious to an impending onslaught.

Hundreds of men, women and children marched along the city’s Martyrs Square chanting anti-Gadhafi slogans, firing guns into the air and berating the international community for not imposing a no-fly zone. Thumping revolutionary anthems blared from a loudspeaker just hours after the airport was bombed.

“Nobody is afraid,” said Ramadan Budarra, 28, a construction company safety officer. “Look, even the women are out demonstrating. Gadhafi can’t even take Ajdabiya, so how can he even come close to Benghazi?”