KABUL, Afghanistan — NATO and the Afghan military are about to launch their biggest joint offensive of the war, and they appear to be making sure the Taliban know they are coming.

On Wednesday, spokesmen for the Afghan Defense Ministry and for the NATO forces announced at a news conference that an offensive involving thousands of troops would begin “in the near future,” and while they did not confirm the place, they also did not dispute widespread speculation that the target was the Taliban-held town of Marja.

The deliberate publicizing of the offensive — with news conferences, press releases and public pronouncements — is relatively unusual for the military. There could be several strategic benefits — and risks. If Taliban were to withdraw in advance of the offensive and civilians had ample warning, there could be fewer military and civilian casualties.

“In some cases it may make sense, with a population-centered strategy, to give an awareness where U.S. and Afghan forces are going, and give an opportunity for Taliban and insurgent forces to clear out,” said Seth Jones, a RAND Corporation senior political scientist who specializes in Afghanistan. Gen. Stanley A. McChrystal, the American military commander in Afghanistan, has emphasized a counterinsurgency strategy that focuses on reducing civilian casualties and convincing the local population that the Americans and NATO can protect them.

Afghan military officials and Marja residents say that the area has been heavily leafleted to warn civilians that an offensive is coming.

But forewarning also gives the Taliban an opportunity to escape and regroup elsewhere, as insurgents in Iraq did after the 2004 American Marine assault on Falluja. That assault was also widely expected, and the timing generally known within days. Already, Mr. Jones said, there have been reports of Taliban militants filtering out of Marja. Alternatively, the Taliban could fortify their defenses and plant explosives around the area.

The imminent offensive was first announced in a press release from the Pentagon on Monday, and, unusually, the name of the campaign was disclosed: Operation Moshtarak, which means Joint Operation in Dari.

While reporters embedded with American units in southern Afghanistan have been told not to mention the target of the offensive in their dispatches, or in e-mail or phone calls, even Taliban commanders have said they expect their Marja stronghold to be attacked soon.

For months, the town has been under complete Taliban control, and more than a thousand Taliban reportedly took refuge there beginning last summer, as United States Marines stepped up the pressure in Helmand Province. Located in the opium poppy-growing belt, Marja also is close to the strategically important provincial capital, Lashkar Gah, and has been a staging area for suicide attacks and other bombings.

A local Taliban commander in Marja reached by cellphone said they were aware that the town was the target, and he sought to signal that they would not be intimidated. “We will definitely defend Marja,” said the commander, who goes by the name Ishaq. “It’s the only place left for us. We have all of our fighters assembled here to fight against Afghan and foreign forces.”

“We know this operation will be much bigger than previous operations,” Mr. Ishaq said. “We are determined to fight until the last drop of our blood.”

At the news conference on Wednesday, Brig. Gen. Zahir Azimi, spokesman for Afghanistan’s Ministry of Defense, said the offensive would start “in the near future” in southern Afghanistan. Brig. Gen. Eric Tremblay, the spokesman for NATO forces here, was more specific, saying it would be in central Helmand Province. “There will be at least a thousand Afghan National Police, thousands of Afghan National Army soldiers and many thousands of ISAF troops,” General Azimi said, using the acronym for the International Security Assistance Force.

Since summer, international forces led by the United States Marines have been systematically clearing the Helmand River valley, and in December their Operation Cobra’s Anger forced Taliban fighters out of the town of Now Zad, leaving Marja as the last town under Taliban control.

“It’s no secret we’re going there,” the Marine commander in Helmand, Brig. Gen. Larry Nicholson, said in an interview with Reuters and CNN in December. “There’s an inevitability that there’s a date with destiny with Marja, and we’re moving toward that.”

At the bus station in Lashkar Gah on Wednesday, Marja residents said the offensive had been expected since leaflets were dropped from helicopters beginning about four months ago. The leaflets warned residents to stay off the streets after 9 p.m. and to stay away from windows once an offensive started.

Ahmed Shah, a 53-year-old driver, said that Taliban fighters had been increasing their numbers in Marja in recent days and residents expected an attack soon, although they did not know when. “Their activities are visible in the city and it seems they are preparing for face-to-face fighting with the government and international forces.”

“We know about the operation but we don’t know how big and how powerful it will be,” said Azizullah, 35, a shopkeeper from Marja, who uses only one name. “It seems it will be a major operation because compared to the previous time, this time there’s too much preparation for this operation on both sides.”

Both Mr. Azizullah and Mr. Shah said they were hopeful that Afghan government and international forces would stay in Marja, rather than pulling out after a short time, as happened the last time the coalition took Marja, in May 2009.

“There will be a big clearance operation and we will separate the civilian population from the insurgents,” General Azimi said. “As I’ve said many times before, we will have a bloody summer ahead.”

General Tremblay said there was no intention of leaving the area after the offensive. Government and civilian reconstruction efforts will follow closely behind the military campaign, he said.

General Azimi said the Afghan military would be bringing troops in from many parts of the country for the offensive. In addition, American troop strength has doubled in the course of the past six months, making it easier to remain in force in areas that are cleared of Taliban.

He said previous efforts to clear the Taliban from areas in Helmand Province faltered because there were insufficient troops to stay permanently.