In a speech on the NATO website, Rasmussen said the fighting force will be part of an overall Readiness Action Plan that "responds to Russia's aggressive behavior -- but it equips the alliance to respond to all security challenges, wherever they may arise."
He said this "spearhead" force would be able to "travel light, but strike hard if needed."
NATO will look at possible upgrades to infrastructure that could include airfields and ports, he said.
New bases will be set up and equipment pre-positioned at bases, a NATO diplomatic source said.
"We are also facing crises to the southeast and south," said a senior NATO official. The plan "needs to be able to deal with all crises that we might be facing in the future from wherever they might come."
Rasmussen said President Petro Poroshenko of Ukraine will attend the summit and NATO will "make clear our support for Ukraine."
Also on Monday, UK Prime Minister David Cameron told Parliament that the presence of Russian soldiers on Ukraine soil is completely unjustified and unacceptable.
"Russia appears to be trying to force to Ukraine to abandon its democratic choices through the barrel of a gun," he said.
Cameron said new sanctions measures will be drawn up by the EU within a week.
Ukraine airfield attack reported
A Russian army tank attacked airfields in eastern Ukraine on Monday, Ukrainian military officials said, amid worsening tensions between Kiev and Moscow.
A battle is under way at the airport of the eastern city of Luhansk, Ukrainian counter terrorism officials said.
Shortly before the attack, Russia urged the Ukrainian military to retreat from civilian locations in the east, saying pro-Moscow separatists in the region will not disarm for fear of getting killed.
The same day, Ukraine said one of its patrol boats was capsized and two of its crew are missing off the coast of the city of Mariupol. Officials did not say who was behind the attack.
Poroshenko has said thousands of Russian troops are in his nation's east, helping the separatists.
Though Russia has denied sending its troops to Ukraine, it defended the rebels' action in the east.
"Washington and Brussels need to ask Kiev authorities to stop shelling the houses, schools, hospitals and so on because you leave militia with no choice but to stand up to protect their people," Russian Foreign Minister Sergei Lavrov said.
Lavrov: 'Let us sit down and talk'
"Let's not ask militia to lay down their weapons and allow themselves to be killed."
Lavrov said negotiations, not threats, will help resolve the crisis between the two neighbors.
"Let us sit down and talk instead of threatening with sanctions and stubbornly making absolutely unrealistic demands of the militia laying down arms," he said. "This is what the peace plan of Poroshenko is about."
Russian President Vladimir Putin sparked controversy when he talked about "statehood" for eastern Ukraine.
"Substantive meaningful talks related to the issues of society's political organization and statehood in southeastern Ukraine should start immediately in order to protect people living there," Putin said Sunday.
The Kremlin later denied that Putin was calling for statehood in the region, saying he was referring to inclusive talks with all sides represented.
Russia annexed Ukraine's Crimean Peninsula in March following the ouster of President Viktor Yanukovych the previous month.
Violence broke out in the eastern Donetsk and Luhansk regions in April when separatist leaders declared independence from the government in Kiev. Since then, the conflict between the pro-Russia rebels and the Ukrainian military has killed 2,500 people, according to the United Nations.
U.S. lawmaker visits Ukraine
A U.S. lawmaker called for the arming of Ukrainian forces along the eastern border.
Sen. Robert Menendez, D-New Jersey, is in the Ukrainian capital of Kiev. He said the conflict in eastern Ukraine is not a rebel uprising, but a Russian invasion.
"We should be providing the Ukrainians with the type of defensive weapons that will impose a cost upon Putin for further aggression," said Menendez, chairman of the Senate Foreign Relations Committee.
In the past, U.S. President Barack Obama has opposed supplying Ukraine with weapons. .
Poroshenko warned that his nation's crisis with Russia has worsened, and is inching closer to a "full-scale war."
The European Union has demanded Moscow withdraw its troops or face additional sanctions.
European Council President Herman Van Rompuy said new sanctions are in the works for Russia. Proposals will be ready for consideration in a week, he said over the weekend.
CNN's Victoria Butenko reported from Kiev, and Faith Karimi wrote and reported in Atlanta.
By Ralph Ellis, Faith Karimi and Victoria Butenko