John C. Whitehead is minding the store today at Foggy Bottom. With Secretary of State George P. Shultz at President Reagan's side in Tokyo, the deputy secretary stands in his shoes for the 101st day since he began his job last July.

With no real issues or regions to call his own in a specialist's world, State's second highest-ranking official is out of the turf tussles and the gossip mills at the department -- to the point, perhaps, of being the perfect No. 2. Though he is acting secretary in Shultz's absences, Whitehead is the first to say, "I don't like to make too much of it." Shultz remains in charge of all policy decisions, no matter where he goes.

Yet Whitehead and Shultz have communicated every day of this trip by cable or secure telephone, and throughout the disastrous events at the Chernobyl nuclear power plant, Whitehead has been the administration's main coordinator on the matter.

"We've been very disappointed in the Soviets" he says. "We hoped they would be more open in supplying us with information. We're challenging them in the interest of humanity to tell us, and we are asking them to permit our own medical teams to come in and make their own investigation."

Whitehead, 64, doesn't have the manicured looks or reserved demeanor of a diplomat. As he sits in his elegant office at the State Department, his navy suit is slightly rumpled and baggy, and his silver hair shoots out at odd angles. The fact is, this erstwhile investment banker didn't want this job -- and doesn't know exactly how he got it.

"I'm not sure how he found me," he says of his boss, Shultz. "I worked at Goldman, Sachs 38 years and was busily involved in early retirement [Whitehead] had been cochairman when he called and asked me if I would come down the next day and talk to him . . . . He didn't tell me that I was even being considered for a job. He said he wanted to talk to me about a matter of urgent national importance. I guessed that some Latin-American country must be going bankrupt."

That was last April, and within hours Shultz and President Reagan had asked Whitehead to become Shultz's deputy.

Why a banker? What does Wall Street have to offer Foggy Bottom besides firsthand experience with Third World debt?

"Investment bankers," Shultz explained when he announced the appointment, "tend to get involved when the big deals come along." They have to "absorb enormous amounts of material quickly," the secretary added later, "size up situations accurately and make a decision that will stick."

It also seems probable that Whitehead's financial expertise appealed in other ways to economist and former treasury secretary Shultz, who is clearly happiest dealing with economic issues. There are few if any diplomats in Foggy Bottom who approach Shultz's expertise, but Whitehead can and does offer him original perspective and a knowledgeable sounding board on global money matters.

At first, Whitehead insisted that he was not qualified to accept the job offer. Today, he is thriving in his second career.

He began to make an international name for himself last October on a delicate fence-mending mission to Italy and Egypt after the Achille Lauro hijacking and the U.S. decision to force down an Egyptian plane carrying the hijackers. It was Rome on Saturday and Cairo on Sunday, consoling and patching as he went along.

More recently, he traveled to Europe after the U.S. air strikes at Tripoli to talk to allies -- this time with a tougher line. "One of the results of the military action has been that it has shaken up our allies and made them recognize that it's important for them to cooperate in nonmilitary actions against Qaddafi -- political action and economic actions."

Whitehead made some waves on this subject last December at a news conference not long after the attacks on the Rome and Vienna airports, with remarks contradicting what was then the administration's stand of reluctance to call for sanctions. The incident led reporters to press a State Department spokesman to clarify the department's position.

Whitehead concedes that policy coordination and restraint have been among the more challenging aspects of his job.

"I have to be very careful," he says, "not to drift into giving too much of my own opinion."

Whitehead's straight-speaking style has caused more than one controversy. One of his goals at State has been to mend relations between the department and its conservative critics -- and at least for a while, he seemed to be doing fairly well. In December, he invited 11 officials and trustees from the conservative Heritage Foundation to State to voice their views, and he was instrumental in having a career foreign service officer assigned to Heritage as a "diplomat in residence."

But in January, the foundation blasted administration foreign policy in a no-slams-barred paper entitled "Rhetoric vs. Reality: How the State Department Betrays the Reagan Vision." Whitehead blasted right back.

The report, Whitehead told Heritage trustees in a letter that became public, was "filled with misstatement, inaccuracies and false "Maybe one is better off not to know all the nuances, but to come right to the heart of the matter -- and that's what I try to do." innuendos . . . uninformed polemics and mischievous gossip . . . . I am really ashamed to have been a regular contributor." In its most controversial part, Whitehead's letter -- written on a State Department letterhead -- urged the foundation's trustees to resign in protest.

"I don't consider myself a right-wing Republican," he says, "but pretty close." However, he adds, he didn't intend his letter "to become a public controversy."

Whitehead was born in Evanston, Ill., and grew up in Montclair, N.J.; his father was an AT&T executive. He graduated from Haverford College in 1943, joined the Navy and, following the war, received an MBA from the Harvard Business School. Whitehead joined Goldman, Sachs & Co. in 1947 as a statistician and rose to the cochairmanship, along with John Weinberg, in 1976. He has three children -- a son and daughter in their thirties and another daughter in her teens -- all living in New York.

On Wall Street, Weinberg and Whitehead were known as Mr. Inside and Mr. Outside, perfect complements to each other. Weinberg was the company man, the administrator; Whitehead was the outside envoy, the man who represented the firm to the world and brought in the business.

"He did his own thing at a firm which prided itself on team playing," says an executive of a competing firm. "And it worked."

"John Whitehead was really one of the major figures on Wall Street in the past two decades," says Samuel Hayes, who teaches investment banking at Harvard. "His reputation as an excellent manager of people has to effectively translate into what he is now doing at the State Department."

Whitehead is said to have placed a high premium on business ethics, believing more business would come if the firm developed a strict code and stuck by it. Goldman, Sachs, for example, generally refuses to represent companies involved in hostile takeovers, an unusual policy for a major Wall Street firm. Whitehead "was instrumental in that decision," says Hayes, "and it created an image of the firm which many of their clients found attractive."

Whitehead's tendency to say what he thinks has underscored his non-diplomat's status and he is regarded by many working bureaucrats at State as a well-meaning, intelligent amateur. From sheer inexperience in Washington, he has not yet become involved in deep political maneuvering with members of Congress. But everything suggests he would do well at it if he did.

"An investment banker does a lot of negotiation," he says. "I've negotiated hundreds of big transactions and dozens of mergers . . . . it comes naturally to me. So that part of diplomacy has been relatively easy."

He dismisses the notion that he hasn't mastered the subtleties of his new turf.

"Maybe one is better off not to know all the nuances," he says, "but to come right to the heart of the matter -- and that's what I try to do. Those who get bogged down by nuances sometimes miss the forest for the trees.