NAIROBI (Reuters) -is being sucked back into to open another front against Islamist rebels battling Kenyan forces but even a military victory is unlikely to end two decades of anarchy unless the country's feuding politicians and clans want peace.
An Ethiopian government official acknowledged for the first time on Friday that a small force had already rolled across the border and was carrying out reconnaissance missions ahead of a full deployment that would last "weeks.
"We are looking at a brief period of time, weeks. We don't want our deployment to be used for propaganda by the extremists," the official told Reuters, declining to be named.
"The aim is to support (Somalia's) Transitional Federal Government troops and their allies to expand their control in the south of Somalia and pull back," he added.
Head of the regional IGAD bloc, Mahboub Maalim, said Ethiopia had promised to "assist in the peace and stabilization activities" ongoing in Somalia.
has leaned heavily on Ethiopia to send a force to join the assault against the al Qaeda-linked al Shabaab rebels.
Ethiopian troops are unlikely to stray far this time, aware their last intervention in 2006-2009 to flush out another Islamist group was a rallying call for the militants, who portrayed Ethiopia as Christian invaders in a Muslim country.
Kenya too has stressed it will leave Somalia once it has dismantled al Shabaab's network and seized strongholds that provide the insurgents a financial lifeline, potentially leaving a void for former warlords to step into.
Somalia is a hotspot in the global war against militant Islam. But in the two decades since warlords and then Islamist insurgents reduced its government to impotence, a string of foreign forces, including American, have failed to bring order.
"The Ethiopians can be none too happy with the state of affairs," said J. Peter Pham, Africa director with U.S. think-tank the Atlantic Council.
"The Kenyans, having foolishly charged in with apparently little thought as to realistic strategic objectives... are now bogged down and need an additional front opened against al Shabaab to relieve the pressure on themselves," he said.
Kenyan forces crossed into Somalia nearly six weeks ago in an incursion designed to dismantle the militants' network.
While they initially advanced smoothly on rebel strongholds in southern Somalia, the Kenyan campaign has stalled as al Shabaab fighters melt into the population, while heavy rains and muddy terrain swamp its forces.
ONCE BITTEN, TWICE SHY
Ethiopia is reviled across much of Somalia.
With tacit U.S. backing, and at the invitation of the beleaguered Somali government, Ethiopia blitzed its way through Somalia in late 2006 and 2007 to rout another Somali Islamist administration from de facto power.
Washington said the Islamic Courts Union (ICU) had ties to al Qaeda. It now backs a government led by a former ICU boss.
Al Shabaab rose from the broken ICU, its ranks swollen by a deep resentment at the perception of Ethiopia as a Christian invader in a Muslim country.
"The Ethiopians understand all too well that their presence, as a Christian nation, in Somalia could be propaganda for al Shabaab," said an African Union official in Addis Ababa.
"They're not going to repeat that mistake twice," the official said on condition of anonymity. "They will back up ASWJ, equip them, train them and not stray too far," referring to the pro-Mogadishu Sufi militia group, Ahlu Sunna Waljamaca, which is also closely allied to Ethiopia.
A second AU official said Ethiopian troops might push as deep as Baidoa, about 250 km (155 miles) northwest of Mogadishu with an airport, to stretch rebel lines and cut off some supply routes.
An Ahlu Sunna commander told Reuters the militia expected Ethiopia to train 4,000 fighters.
Kenya boasts it could seize Kismayu, a nerve-center for rebel operations and prized Kenyan target, any time it chooses.
The advance on the port city was still on and the country's navy has blockaded the sea port, a Kenyan military source said. Kenya hopes to starve the militants of huge revenues on inflows of smuggled contraband and charcoal exports to the Gulf.
The lack of a significant blow to the rebels so far, though, has raised questions about Kenya's troops numbers and strategy.
In 2006, against Ethiopia, a military giant in the region, the insurgents squared up to the offensive and suffered.
"This time, they faded among the population ... even as they draw (Kenya) deeper into Somalia, extending their lines of communication and supply and allowing them to get bogged down in the unforgiving terrain," Pham said.
Some Western diplomats believe Kismayu will fall, but acknowledge their are few answers to the question: What next?
"I don't think even within the political and military circles anyone can tell you the end game, the exit plan," Ndung'u Wainaina, head the Nairobi-based think-tank International Center for Policy and Conflict said.
Kenyan troops might seek to switch berets and join an African peacekeeping force. That, though, would require the United Nations to extend the force's mandate beyond Mogadishu and raise the ceiling on troop numbers from the current 12,000.
Western powers -- most likely the United States and European Union -- would also need to stump up more cash.
"It's difficult to see how that could happen anytime soon given that the salaries of the soldiers are paid for by the West. There's no stomach for giving any more money to AMISOM," said a Western diplomat working in the region.
Even if Kenya and its regional allies crush the rebels, military force at best provides breathing space.
Critical is political reform, but Somalia's government has done little to convince its neighbors it is capable of extending its sphere of power beyond the capital.
The unelected government's legitimacy is already battered by internal power struggles and corruption. Its reliance on yet another foreign incursion might damage its credibility yet further if there is no swift political follow up.
"There is a very real danger that al-Shabaab gets defeated only to be replaced by nothing better than a collection of warlords whose depredations gives rise to yet another insurgency, renewing the cycle of conflict and prolonging once more the sufferings ordinary Somalis," said Pham.
(Additional reporting by Abdi Sheikh in Mogadishu, Barry Malone and James Macharia in Nairobi and Aaron Maasho in Addis Ababa; editing by David Clarke and Philippa Fletcher)