Adm. William James Crowe Jr., who this week begins steering the Joint Chiefs of Staff through what may be their most perilous passage in three decades, can be witty, intellectual and tough. But above all he is a skilled practitioner of the art of the possible.

"My father used to say, 'Your mind is like a parachute. If it won't open when you need it, it is not much good.' I have an open mind."

Other Croweisms charmed Democrats and Republicans at the admiral's confirmation hearing before the Senate Armed Services Committee, where Sen. Sam Nunn (D-Ga.) called him "the right man in the right place at the right time." Crowe's two-to-four-year tenure as chiefs chairman, the nation's preeminent military officer, begins Tuesday.

"My minister," quipped the 60-year-old Crowe, in a colloquial aside to the committee, "said that the difference between a eulogy and a testimonial is that in the case of the testimonial there is one man in the audience who believes it."

Crowe (rhymes with "brow") is seen by some as potentially the U.S. military's most articulate and appealing spokesman in years -- a smooth, post-World War II warrior-statesman, who holds a doctorate from Princeton and who many believe offers the best hope of coping with a potential landslide of problems and issues about to come crashing down on America's military establishment. They include:

*The breakup of the prodefense constituency, as Congress slams on the brakes after four years of record peacetime Pentagon budget increases.

*Fundamental decisions on arms control, ranging from observance of the second Strategic Arms Limitation Treaty (SALT) to the militarization of space.

*Increasing pressure on the military to preempt terrorist attacks and find ways to retaliate without killing innocent civilians.

*Rumbles of impending political chaos in the Philippines where the huge U.S. bases at Subic Bay and Clark Field may be in jeopardy at a time when Soviet power in the Pacific Ocean has expanded.

*Congressional action to overhaul the joint chiefs, which could be the biggest structural change in the military hierarchy since the Defense Department was created in 1947.

Is Crowe, who arrives in Washington after four years of commanding U.S. forces in the Pacific, up to all the challenges facing the military establishment?

"He's the best we've got," said one of his Navy contemporaries. "The only place he's weak is in operational experience. He hasn't done anything at sea since he was a lieutenant commander on a diesel submarine. But he's smart enough to put people around him who are operators and, better yet, to listen to them. Bill has been buried professionally several times. But here he is on top."

A Crowe aide said the admiral plans to assume the chairmanship quietly in hopes of projecting an image inside and outside the Defense Department of a cautious executive whose decisions reflect consensus opinions, like his predecessor, Army Gen. John W. Vessey Jr.

But Crowe, an experienced Washington hand, is expected to be much more active than Vessey in building bridges all around him -- including links to the severest congressional critics of the Pentagon's rearmament program. His style has always been that of a compromiser, a seeker of middle ground, rather than a dogmatic authoritarian, according to assorted Crowe-watchers.

Twenty years ago at Princeton, in his doctoral dissertation on "The Policy Roots of the Modern Royal Navy 1946-53," Crowe, who at that time wore only the three stripes of a Navy commander, articulated in somewhat pedestrian prose his philosophy about why the military must be flexible to be responsible:

"When the military is inflexible and finds itself incapable of accommodating to the changing moods and conditions of the nation, it not only weakens the government's external influence, but may very well become a source of serious domestic discontent."

He also has resisted sounding alarms of "the Russians are coming," in contrast to some recent statements from the White House and Pentagon.

"I do not consider the balance deteriorating," he said this summer in discussing his vast command in the Pacific. "It is improving in my region." He added that it would be senseless to try to match the Soviets "weapon for weapon, man for man, plane for plane" all over the world.

"If we had to fight the Soviets, we would do it in a thoughtful and rational way, and where they are the weakest and where it will influence the outcome the most, and do it in a smart way, concentrating our forces and using our mobility and using our strength," he said.

A Pentagon critic of current Navy strategy, who espouses hitting the Soviets "where they ain't" rather than sending aircraft carriers into the teeth of Soviet defenses, said, "Maybe Crowe can keep the Navy from sailing into the Kola Peninsula" due north of Leningrad.

Crowe, a big man whose frame makes his uniform look slightly rumpled, is one of the few Navy officers to climb high on the career trellis after rejecting offers from the autocratic Adm. Hyman G. Rickover to move up from diesel to nuclear submarines. The native of La Grange, Ky., took the academic-and-policy route instead of the seaborne one. After graduating from the U.S. Naval Academy in 1946, Crowe earned a master of science degree from Stanford University in 1956, a master of arts degree from Princeton in 1964 and a doctorate from Princeton in 1965. That career path usually leads no higher in the Navy than the rank of commander or captain.

"You'll notice," quipped a longtime associate, "that his doctorate from Princeton is in politics, not political science."

At the top of Crowe's agenda will be the Pentagon budget. After voting a trillion dollars for defense during President Reagan's first term, Congress is balking at adding to the current $300 billion a year.

The White House Office of Management and Budget estimates that the Army, Navy, Air Force and Marine Corps will have to rearm with $300 billion less than the administration anticipated in the next five years because future Pentagon budgets will grow at about 3 percent annually above the inflation level. Many members of Congress believe the reduction more likely will be closer to $750 billion.

For Crowe as chairman, the lowered expectations mean trying to keep peace between the service chiefs -- who also sit on the Defense Department's corporate board known as the Joint Chiefs of Staff -- as they fight to save prized programs from the budget ax.

Nunn, ranking Democrat on the Senate Armed Services Committee, has already told Crowe that he must take the lead in "managing and marshaling our resources in a coherent way."

Crowe also will face congressional attempts to overhaul the generous military retirement system, reforms that may make recruiting even more difficult as the available pool of qualified young Americans drops sharply.

Events are likely to force Crowe to take a larger role on arms control issues than did Vessey, who served as chairman for almost four years without having to take any harder position than listing the pros and cons of continuing to observe the SALT II limits on nuclear missile launchers.

The president and Congress soon will ask Crowe and the chiefs to comment not only on the advisability of abiding by SALT II but also on the scrapping or amending of Anti-Ballistic Missile (ABM) Treaty with the Soviet Union. If SALT II limits are scrapped, the chiefs will have to judge whether the resulting unlimited number of warheads jeopardizes Reagan's dream of a space-based strategic defense against nuclear missiles.

Crowe is an old hand at wrestling with strategic tradeoffs, experience that includes a tour in 1974 as the Navy's deputy director of strategic planning.

He is on record as favoring the so-called Star Wars research, but has not been asked whether its promise outweighs the advantage of keeping the ABM treaty intact.

Pentagon concerns about Soviet muscle in the Pacific stem largely from the large Soviet base at Camranh Bay in Vietnam.

"In the old days," said a senior officer from Crowe's Pacific command, "we could have compensated for losing Subic and Clark by building up Guam. But we can't do that now with the Russians in Camranh."

Crowe will almost certainly be asked by the Reagan administration to work with Philippine officials to save the bases at Subic and Clark. Navy officers said he so impressed Reagan last year in Hawaii, when he gave the president a 90-minute briefing without notes on the challenges in the Pacific, that the president remarked to Weinberger, "If we ever need a new chairman, this is the guy."

On the issue of preemptive attacks against terrorists, Crowe told the Senate Armed Services Committee: "My general principle would be to try in the best manner available to determine whether the situation would be better off after we had done it or worse off. If we were better off, the answer is obvious."

The joint chiefs were reluctant to retaliate for the 1983 bombing in Beirut that killed 241 U.S. servicemen for fear it would reap more deadly attacks against exposed Marines at the airport.

Overhanging such international issues awaiting Crowe is the proposed reorganization of the joint chiefs.

Under a compromise bill the pending at the House Armed Services Committee, Crowe's job would be considerably bolstered, potentially giving him the most powerful military voice since the job of chairman of the joint chiefs was created in 1949.

The chiefs have a staff of 400, which critics contend is hamstrung by interservice rivalry.

The Navy, for example, could veto an Air Force proposal to study the vulnerability of aircraft carriers in the age of reconnaissance satellites and "smart" weapons that can be fired dozens of miles from their intended target.

The House bill would put the staff under the single direction of the chairman. He could use this staff in recommending to the secretary of defense and president ways to get more bang for the buck, to deploy forces differently around the world, or to make the case for giving one service a bigger slice of the money pie at the expense of another. Under the proposed reform, orders from the president and defense secretary would go through the chairman alone, rather than through the service chiefs. One objective, according to architects of the bill, is to keep military operations from becoming a four-service show -- as happened in the hostage rescue attempt in Iran and the invasion of Grenada -- when sound military logic may prescribe a more restricted action.

Thus, Crowe in his first two years as chairman would be shaping the structure of his own job and that of his successors in ways affecting the efficiency of the U.S. military for the foreseeable future.

He is on record in written remarks to the House Armed Services Committee as saying that unified commanders, such as those commanding all forces in the Pacific and Atlantic, should have more clout in building the Defense Department budget, as well as more direct lines to top decision makers in Washington.

Crowe, who has told friends at several points in his life that he believed his Navy career was at a dead end, is fond of citing a Chinese proverb: "Prediction is very difficult, particularly with regard to the future."