SEOUL (Reuters) - North Korea said on Friday it will reopen a military hotline with the South, a move suggesting the secretive state may be tempering recent harsh rhetoric ahead of a widely condemned missile launch expected early next month.

The hotline, the only telephone link between the two Koreas, will reopen on Saturday, a day after U.S. and South Korean troops end annual defense drills that Pyongyang has called preparations for an invasion.

North Korea had stopped responding to calls on the hotline at the start of the drills on March 9.

Our side will be restoring the military communication line starting at 8 a.m. on March 21 based on the position and intent of militarily guaranteeing the historic joint North-South declaration, the North said in a message to the South.

The declaration refers to a June 2000 statement signed by the South's then President Kim Dae-jung, a liberal, and North Korean leader Kim Jong-il to improve ties and begin commercial exchanges after decades of animosity following the 1950-53 Korean War.

North Korea has directed much of its fury over the past few months at conservative President Lee Myung-bak, who ended a decade of no-questions-asked aid and made it conditional on the North moving on pledges to stop trying to build nuclear weapons.

Tension on the peninsula escalated further with the North's announcement it would launch a satellite between April 4 and 8.

Officials in Seoul and Washington say the launch is really a disguised test of its long-range Taepodong-2 missile and warned of punishment under a 2006 U.N. Security Council resolution that forbids Pyongyang from pursuing missile development.

Japan is expected to be in the path of any launch and plans to approve steps to destroy any rocket that falls onto its territory, Kyodo news agency said this week.

On Friday, the North again blocked access by South Korean managers and supplies to a shared factory park on its side of the heavily armed border, the third time it has done so in the past two weeks.

South Korea repeated its criticism that such closures are in violation of agreements signed by the two Koreas and said it puts the North's commitment to the factory project in doubt. Seoul did not say how it would hold Pyongyang responsible for any losses.

Mostly small South Korean firms run factories in the Kaesong park using cheap North Korean labor to produce items such as pots, watches and apparel. Some of them have seen supplies dry up as the North repeatedly blockaded the factory zone.

North Korea's official KCNA news agency said its newly elected Supreme People's Assembly will meet on April 9 in what analysts said would be a landmark session and give leader Kim Jong-il a fresh mandate to press on with militarizing the state.

Kim is expected to be renamed as chairman of the powerful National Defense Commission and may realign the council to begin laying the groundwork for the transfer of power to one of his three sons, analysts said.

But there was no word from the North about two U.S. journalists detained by guards at its northern border with China earlier this week.

The pair were filming across the Tumen River when guards took them into custody, a State Department official said, adding the United States was in touch with the North seeking their release.

(Editing by Paul Tait)