Anders Fogh Rasmussen said the organisations's summit in Cardiff next week would overcome divisions within the alliance and agree to new deployments on Russia's borders – a move certain to trigger a strong reaction from Moscow.
He also outlined moves to boost Ukraine's security, "modernise" its armed forces and help the country counter the threat from Russia.
Rasmussen said: "We will adopt what we call a readiness action plan with the aim to be able to act swiftly in this completely new security environment in Europe."
We have something already called the NATO response force, whose purpose is to be able to be deployed rapidly if needed.
Now it's our intention to develop what I would call a spearhead within that response force at very, very high readiness.
"In order to be able to provide such rapid reinforcements you also need some reception facilities in host nations. So it will involve the pre-positioning of supplies, of equipment, preparation of infrastructure, bases, headquarters. The bottom line is you will in the future see a more visible NATO presence in the east."
Poland and the three Baltic states have been alarmed at the perceived threat from Russia and have been clamouring for a stronger NATO presence in the region.
They have criticised what they see as tokenism in the alliance's response so far.
But the issue of permanent NATO bases in east Europe is divisive.
The French, Italians and Spanish are opposed while the Americans and British are supportive of the eastern European demands.
The Germans, said a NATO official, were sitting on the fence, wary of provoking Russia.
The Cardiff summit is likely to come up with a formula, alliance sources said, which would avoid the term "permanent" for the new bases.
But the impact will be to have constantly manned NATO facilities east of what used to be the iron curtain.
"It can be on a rotation basis, with a very high frequency. The point is that any potential aggressor should know that if they were to even think of an attack against a NATO ally they will meet not only soldiers from that specific country but they will meet NATO troops. This is what is important," said Rasmussen.
The only NATO headquarters east of the old cold war frontier is at Szczecin, on Poland's Baltic coast.
Sources said this was likely to be the hub for the new deployments.
Air and naval plans had been completed, but the issue of international land forces in the east was proving trickier to agree upon.
Asked whether there would be permanent international deployments under a NATO flag in east Europe, Rasmussen said: "The brief answer is yes. To prevent misunderstanding I use the phrase 'for as long as necessary'. Our eastern allies will be satisfied when they see what is actually in the readiness action plan."
Rasmussen said the forces could be deployed within hours.
NATO has clearly been caught napping by the Russian president's well prepared advances in Ukraine since February and is scrambling to come up with strategies for a new era in which Russia has gone from being a "strategic partner" of the alliance to a hostile actor perfecting what the alliance terms "hybrid warfare".
Rasmussen, whose term as NATO chief is coming to an end, said: "We have to face the reality that Russia does not consider NATO a partner. Russia is a nation that unfortunately for the first time since the second world war has grabbed land by force. Obviously we have to adapt to that."
In an interview with the Guardian and five other European newspapers, he said: "It is safe to say that nobody had expected Russia to grab land by force. We also saw a remarkable change in the Russian military approach and capability since, for instance, the Georgian war in 2008.
"We have seen the Russians improve their ability to act swiftly. They can within a very, very, short time convert a major military exercise into an offensive military operation."
Rasmussen reiterated that the Russians had massed in their thousands on Ukraine's eastern borders, and had been firing artillery into Ukraine.
His information was based on NATO's own intelligence and "multiple reports".
But NATO officials admitted that the intelligence was impaired by a lack of solid information from the ground.
"We can only watch from 23 miles up," said an official.
Rasmussen said: "We have reports from multiple sources showing quite a lively Russian involvement in destabilising eastern Ukraine.
"We have seen artillery firing across the border and also inside Ukraine. We have seen a Russian military buildup along the border. Quite clearly, Russia is involved in destabilising eastern Ukraine … You see a sophisticated combination of traditional conventional warfare mixed up with information and primarily disinformation operations. It will take more than NATO to counter such hybrid warfare effectively."
If western leaders have been surprised and also impressed by the sudden display of Russian military prowess, Ukraine, by contrast, is in a pitiful condition militarily, according to NATO officials.
"If we are two steps behind the Russians, the Ukrainians are 16 steps behind," said a NATO source recently in Kiev.
"Their generals just want to blow everything up. But it's not a shooting war, it's an information war."
In further moves certain to rile Putin, NATO is to step up its aid to, and collaboration with, the Ukrainian military.
Ukraine's president, Petro Poroshenko, is to attend the Cardiff summit and will be the sole non-NATO head of state to negotiate with alliance leaders.
Four "trust funds" are to be established to finance Ukraine's military logistics, command and control structures, and cyber defences, and to pay the armed forces' pensions.
"Ukraine follows its own path. That will be demonstrated at the summit because we will have a NATO-Ukraine summit meeting," said Rasmussen.
"It is actually what we will decide to do at the summit, to help them build the capacity of their security sector, modernise it."
The summit will also grapple with the perennial question of reduced European defence spending at a time of intense instability on the continent's eastern and southern borders as well as the growing US exasperation with Europe's reluctance to fund its own security properly.
"Since the end of the cold war we have lived in relatively good weather. Now we are faced with a profound climate change. That requires more investment," said Rasmussen.
"Politicians have tried to harvest the peace dividend after the end of the cold war. That's understandable. But now we are in a completely new security situation."
Source: The Guardian