WASHINGTON, April 10 (Reuters) - U.S. President Joe

Biden and Japanese Prime Minister Fumio Kishida on Wednesday

unveiled plans for military cooperation and projects ranging

from missiles to moon landings, strengthening their alliance

with an eye on countering China and Russia.

A joint news conference at the White House reflected the

growing importance of Japan on the world stage and to the United

States, as the two leaders weighed in on Gaza and Israel,

Ukraine and Russia, North Korea and other world flashpoints.

Biden and Kishida brushed off a dispute over Nippon Steel's ( NISTF )

offer for U.S. Steel, saying the issue was not a major factor in

their discussions on a day of White House pomp and pageantry

that culminated in a lavish state dinner.

"This is the most significant upgrade in our alliance since

it was first established," Biden said after about two hours of

talks that focused on the restive Indo-Pacific region and

China's actions.

The United States and its allies, including Japan, have been

bolstering their militaries to counter what they see as a

growing threat from China in the South China Sea and the East

China Sea, and to deter any attempt to seize Taiwan, a

self-ruled Island that Beijing considers its own.

Kishida said the two leaders discussed tense relations

between Taiwan and China, and pledged to uphold international

order based on the rule of law. Chinese leader Xi Jinping

recently said outside interference could not stop the island's

"family reunion" with mainland China.

"Unilateral attempts to change status quo by force or

coercion is absolutely unacceptable, wherever it may be,"

Kishida said. The U.S. and Japan will continue to respond to

such actions, including challenges from China, he said.

"Regarding Russia's aggression of Ukraine ... Ukraine today

may be East Asia tomorrow," Kishida said.

Biden also vowed to keep open lines of communication with

China and said the U.S.- Japan alliance was defensive in nature.

He spoke to Chinese President Xi Jinping last week.

JOINT MILITARY STRUCTURE

The announcements from Biden and Kishida brought the two

World War Two enemies into the closest collaboration they have

had since they became allies decades ago.

Biden said their militaries will cooperate with a joint

command structure and they will, together with Australia,

develop a new air missile defense network. The two leaders also

announced that Japanese astronauts will participate in NASA moon

missions.

Overall, the U.S. and Japan have hammered out about 70

agreements on defense cooperation, including moves to upgrade

the U.S. military command structure in Japan to make it better

able to work with Japanese forces in a crisis.

Japan, often described as the U.S.'s most important Asian

ally and its largest source of foreign direct investment, is

taking on a stepped-up global role after a series of security

law changes in the past decade that have transformed its

pacifist constitution.

Kishida will address the U.S. Congress on Thursday and

join Biden and Philippine President Ferdinand Marcos Jr. for a

meeting expected to focus on Beijing's South China Sea

incursions.

The meeting took place as China steps up pressure on the

Philippines in the South China Sea over areas Beijing claims but

that international law says belong to the Philippines.

China is attempting to isolate Japan and the Philippines, a

U.S. official said. By meeting the leaders of those two nations

this week in Washington, Biden is aiming to "flip the script and

isolate China."

Fitch cut its outlook on China's sovereign credit rating to

negative on Wednesday, citing risks to public finances as the

economy faces increasing uncertainty in its shift to new growth

models.

On Thursday, Biden will also hold a bilateral meeting with

Marcos, whom he welcomed in Washington just last year, before

the pair join Kishida for a trilateral summit.

The visit may give a political boost to Kishida, whose

popularity has waned at home.

He is being greeted with great fanfare, with Japanese flags

on display throughout Washington ahead of the glitzy state

dinner where guests included former President Bill Clinton,

former Secretary of State Hillary Clinton, actor Robert De Niro,

Amazon.com's ( AMZN ) Jeff Bezos and Federal Reserve Chair

Jerome Powell.

Musician Paul Simon provided the entertainment after the

dinner, opening his set with a performance of "Graceland."

Overshadowing the visit is a controversy over the planned

$15 billion acquisition of American steel maker U.S. Steel

by Japan's Nippon Steel ( NISTF ), a deal some say is "on life

support" after criticism by Biden and former President Donald

Trump, his rival in November's U.S. election.

Kishida, asked about the deal, said he hoped discussions

about it would bear fruit.

"We wish to cement this win-win relationship," he said.

Biden said he stood by his commitment to union workers on

the issue.

Also looming are Japanese concerns that if Trump wins a

second term he might seek a deal with China that could

destabilize the region.