NAIROBI, Kenya (AP) _ Rebels captured southern Sudan's second-largest city by pretending to defect so that they could attack from within the garrison town, a rebel spokesman said today.

The Sudan People's Liberation Army seized Wau and the terminus of a railway linking southern Sudan to Khartoum in a hard-fought battle, rebel spokesman Justin Arop said in the Kenyan capital, Nairobi.

The victory would mean the rebel force now controls more land than at any point in its 14-year insurgency.

In the Sudanese capital of Khartoum, government officials acknowledged an attack on Wau but denied the city had fallen. In the past, rebels claims of military victories have proved accurate.

No casualty figures were available, but the SPLA reported taking 108 prisoners.

About 1.5 million people have died from fighting, disease and starvation in Sudan since 1983, when John Garang's SPLA renewed the battle for greater autonomy from the Muslim north for the south's Christians and animists.

In the fight for Wau, SPLA forces were helped by Kerubino Kwanyin Bol, a rebel commander who had defected to the government in April, then rejoined rebels again last month, Arop said.

In addition to the railway terminus, which was critical for resupplying isolated government garrisons, the SPLA claimed to have gained the airport in Wau, 625 miles south of the capital.

The SPLA also seized Zagalona, an army garrison just north of Wau; Marial Ajith, northwest of Wau; Zara to the northeast; and Ariath, a garrison town farther north on the railway line, Arop said.

Because Wau was heavily fortified, the SPLA decided to get fighters inside by pretending they were defecting to Kerubino, Arop said.

About a month ago, the SPLA became convinced Kerubino truly wanted to rejoin the rebellion, Arop said. ``When we were sure that he was serious, that is when we allowed our people to defect to him so we could get them inside,'' he said.

About 2,000 men defected with their families, who were sent to make the ploy more convincing, Arop said. ``They were very brave indeed,'' he said.

Reporters taken on a government-sponsored trip to Wau earlier this month reported that tens of thousands of people had gravitated to the town seeking food and medicine. A government aid official said 7,000 defecting rebels had come with them.

The SPLA fighters initially were allowed to keep their guns, but early Thursday the government became edgy and decided they must give up their weapons, Arop said. Fighting broke out.

``These wins are very significant,'' Arop said. ``Khartoum will have to talk with us now.'' Previous peace negotiations have yielded no results because neither side was willing to compromise.

By bringing Kerubino back to the SPLA side, Arop said the rebels had defeated a government tactic of using southerners to fight southerners.