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"I don't think this is a moment," Secretary of State John Kerry told NBC News' David Gregory on Sunday, on the eve of a critical trip to the restive capital of Ukraine, "to be proclaiming one thing or the other."

In the instant moment, the secretary was fielding a question about whether the Obama administration's fabled "reset" with Russia can officially be pronounced dead. But Kerry's response could equally be seen as a summation of the administration's still-evolving policy on how to counter the weekend's stunning invasion of Crimea by Russian President Vladimir Putin.

The Russian Federation undertook the operation despite a stern warning from President Obama just hours earlier that Moscow would face unspecified "costs" if it violated Ukraine's territorial integrity.

Senior administration officials conceded, in an hour-long background briefing with reporters Sunday night, that Putin's moves to seize control of key installations in the southeastern part of Ukraine had encompassed the deployment of some 6,000 air and naval forces, along with "considerable materiel," and had resulted in the Kremlin establishing "complete operational control of the Crimean Peninsula." "They are flying in reinforcements," said one senior U.S. official on the call, "and they're settling in."

The officials' acknowledgment that Putin's forces are "settling in" for a protracted occupation of Crimea came only a few hours after Kerry had toured the Sunday morning talk shows to convey how strongly President Obama had urged Putin, in their 90-minute telephone call on Saturday, to reverse the action. And even there, Kerry's presentation carried more than a hint of equivocation.

"The president asked Mr. Putin" -- then Kerry caught himself and started over, in an appearance with CBS News' Bob Schieffer -- "in fact, told Mr. Putin it was imperative to find a different path, to roll back this invasion and undo this act of aggression." Kerry at one point even appeared uncertain about the extent of his boss's communication with the Russian leader, telling ABC News' George Stephanopoulos: "I understand there may have been one phone call."

In his brief visit to Kiev, where he will not be staying overnight, Kerry plans to meet with senior officials of Ukraine's new interim government, prominent lawmakers in the Rada legislature, and key members of civil society.

With the country still reeling from the bloody street protests that toppled President Viktor Yanukovych, the Russian ally, from his once solid grip on power, Kerry's interlocutors will be looking to the United States for tangible measures of support in what is, for them, a time of grave crisis.

These include pledges of financial assistance to help with Ukraine's immediate $35 billion deficit and a show of solidarity in the event that Putin is not content to stop at the annexation of Crimea, and seeks to invade eastern Ukraine. Kerry and other senior U.S. officials have said they are responding to the invasion by rallying the leaders of the G-8 group of industrialized nations to isolate Russia economically and diplomatically, including by suspending participation in a planned G-8 session to be held in Sochi later this year.

While Kerry told Stephanopoulos that "the president has all options on the table," a top U.S. official, speaking to reporters hours later, made clear a show of force was not among them, saying: "I don't think we're focused right now on the notion of some U.S. military intervention." Indeed, Kerry himself appeared to acknowledge the limited range of options the U.S. is considering, telling Gregory: "The last thing anybody wants is a military option." At one point Kerry cited to NBC News the fact that the NATO military alliance had issued a "very strong statement" condemning Russia's military operation. "But," the secretary hastened to add, "I don't know what is actually on the table with respect to the steps they may or may not take."

Asked repeatedly if they could give greater clarity to the "costs" that Russia would be made to absorb for the Crimean invasion -- the very punishment that President Obama, in a statement in the White House briefing room on Friday night, warned would be imposed if the invasion proceeded -- Kerry and the senior U.S. officials spoke only in general terms, alluding mostly to the cancellation of scheduled meetings with Russian diplomats, economists, and energy officials.

"There are visa bans, there are asset freezes, there is isolation with respect to trade and investment," Kerry told Schieffer. Later, a senior U.S. official alluded to "the vulnerability of Russian banks" to targeted sanctions, but declined to say affirmatively that the U.S. would actually enact such measures. "We're looking at all of the options," the official said, invoking the mantra of the day.

Kerry and the senior U.S. officials repeatedly told reporters they want to "de-escalate" the Ukraine crisis, and give Putin face-saving opportunities to do so in a way that allows him to reverse course without appearing to have bent to American pressure. At the same time, the Americans routinely disparaged Putin in personal terms and accused the Russian Federation of "hypocrisy" on the world stage.

"When it comes to soft power, the power of attraction," said one senior U.S. official, "Vladimir Putin has no game. So he's left with hard power." "This outrageous action that President Putin has taken," said another, "it's a show of weakness."

At times, Kerry spoke in the unusual, somewhat antiquated style he cultivated across three decades of floor speeches in the U.S. Senate, and which may not be the kind of language most likely to sway a hardened former KGB officer like Putin. "Russia is inviting opprobrium on the international stage," Kerry told NBC, seemingly unmindful that Putin has had no problem courting international "opprobrium" in its support of the Assad regime.

Separately Kerry assured Stephanopolous that the U.S. is prepared to stand up against "hooligans" and "thuggery."

Where the senior U.S. officials spoke most firmly was in bristling at the suggestion that Putin's flagrant disregard for President Obama's warning of Friday evening showed that America's commander-in-chief suffers from "a credibility problem" on the world stage.

"The credibility of the president is manifested in how many leaders and how many countries are joining with us and standing with us in rejecting this Russian action," one official said.