The country's top generals and admirals are set to issue a sobering warning about the world's most powerful military: It is in danger of decline.

The Joint Chiefs of Staff will deliver Tuesday to the Senate Armed Services Committee a series of cautions designed to prompt the White House and Congress to reverse 12 years of declining defense spending, according to several senior military officials.American troops face greater risk fighting the second of two nearly simultaneous wars. Army training could be canceled. The Navy will halt much in-port duty to relieve overworked crews.

And for the first time, units in trouble spots are unprepared for all-out war, according to a top military official. Despite Pentagon insistence that front-line units are ready, some Navy ships and aviation units in the Persian Gulf have reached one of the lowest states of readiness. The shortage of parts and sailors, said the official, is "frankly, a surprise."

Billions more dollars might solve the generals' problems. But money alone, other officers caution, is unlikely to cure all the ills of a military that is smaller than any time since the 1930s and on more missions than anytime since the Vietnam War.

"We take and we take and we take from these kids," said Col. Joseph Byrtus Jr., commander of the 1,000 Marines of the 26th Aviation Group in New River, N.C. "And we never give."

Since 1992, top generals have committed to being able to fight two nearly concurrent conflicts, likely in Korea and the Persian Gulf, insisting they would win quickly.

But citing the length of time it would take forces to reach a second conflict, Gen. Henry Shelton, the chairman of the Joint Chiefs, recently ordered the risk of such a mission to be rated "high" for the first time.

And greater delay could lead to greater casualties. Last year, when risks were judged only moderate, computer models predicted as many as 16,000 Americans wounded and an unknown number dead.

"I think the chiefs are changing their tune," said Sen. John McCain, R-Ariz., a senior member of the Armed Services Committee. "Too much of our military is not ready to rapidly deploy into a conflict."

On Tuesday Shelton is expected to call for more combat training for some units and more long-range transport ships and planes, said a senior military official.

"Who wants to send our forces off to war if they're not trained and ready?" Shelton told reporters recently. "When the call comes, no one ever asks if you're ready to go."

The service chiefs are expected to ask for tens of billions more dollars, according to several military officials. The Army will ask for $5 billion for battalion combat training that otherwise will be canceled. Marines will ask for replacement of 30-year old helicopters.

Announcing a cut in in-port ship duty, the Navy - like the Air Force - will also press for better retirement plans to keep people from quitting.

And service men and women are quitting after being sent abroad for six and seven months at a time - for two and three years at a stretch - watching the demoralizing effects of declining skills and seeing easier, betterpaying civilian jobs.

As the Army has shrunk, its deployments have tripled; on average 30,000 troops were on six-month missions in 80 countries anytime last year. Air Force deployments have quintupled; pilots of F-16 fighters, A-10 attack planes and U-2 spy planes spent 140 days abroad in 1997, most in the Persian Gulf. Today, half the Navy is at sea.

"We are engaged virtually everywhere," Assistant Secretary of Defense Ted Warner, the Pentagon's top civilian strategist, has said. "Ours is an ambitious strategy."

At Minot Air Force Base, N.D., that strategy led the 5th Bomb Wing to fly nuclear deterrence missions, learn to sink ships in the Pacific, dispatch airmen to the Middle East and drill for so many inspections that its 3,500 people worked 120 hours a week, according to a recent study by the RAND Corp.

"It got to the point that it was either people's marriages or their military service," said Col. Robert Elder, the commander. "I told everybody to take a month off."

Many take off for good. The stream of pilots leaving the Air Force for the airlines is growing: from six in every 10 finishing their term of service last year to seven in 10 this year, according to unpublished Air Force figures. Shortly after the turn of the century, the service expects to be 2,000 combat pilots short.

The Navy sends ships to sea with increasingly skeletal crews. The Pacific fleet plies more than 5 million square miles of ocean but is without 17 percent of its junior sailors. As a result, the U.S.S. Abraham Lincoln battlegroup is underway without 400 people, Vice Adm. Herbert Browne told a House panel Friday.

"It really makes everybody work much, much harder," Adm. Archie Clemins, commander of the Pacific Fleet, said in an interview. "It's a crunch."

So, fewer train for all-out war. Only 10 of 14 Army brigades reported last year to Louisiana or the California desert for combat training, according to a survey by the Senate Budget Committee. Seven brigades brought troops; the rest just sent staffs.

"When I first joined the Army, it was train, train, train, shoot, shoot, shoot," said Maj. Ken Strickland, of the Army's elite 82nd Airborne Division. "Now, you train when you can."

Despite demands in Congress and a recent suggestion by President Clinton to spend more on defense, it is unclear the generals will get what they want. Republicans have promised a portion of the first budget surplus in 30 years to tax cuts passed this weekend and Clinton has pledged to fix Social Security.

"I'm not so sure we're not going to be right back here next year," Rep. Gene Taylor, D-Miss., said last week.

Least likely is the thing America's smaller military may need most, fewer missions. Even now, NATO weighs air strikes in Kosovo - and sending in ground troops if a cease-fire is declared.

"I just don't know," said a senior Army official. "I don't know where we'd ever get the people."