"Progress has been made and we encourage it," Rumsfeld said at a news conference with Lithuanian President Valdas Adamkus, who also expressed optimism that Ukraine eventually would join NATO.
On the final stop of a weeklong trip that began in Asia, Rumsfeld joined the defense ministers of nine other NATO countries for a conference Monday to review Ukraine's progress and examine how they can keep Ukraine on track to overhauling and reducing its military.
Washington is pushing hard to help Ukraine, but enthusiasm seems weaker among NATO's other members. Fewer than half of the 26 member countries sent their defense ministers to Vilnius for the conference, which is the fourth in a series of annual meetings.
After meeting with Rumsfeld, Ukrainian Defense Minister Anatoly Gritsenko told reporters that he is confident his government can overcome two other major obstacles to NATO membership: the low opinion that most Ukrainians have of NATO and the opposition in Moscow.
"I don't see it as a really serious issue," Gritsenko said, referring to Russian objections.
He said the Russians have seen that the Baltic states, which joined NATO in 2004 over Moscow's strong objections, do not present the kind of security threat that the Russians had once feared. Lithuania, Latvia and Estonia were part of the Soviet Union until it crumbled in 1991.
In a separate news conference with Rumsfeld, Lithuanian Defense Minister Gediminas Kirkilas said his country's success in raising the level of domestic public support for NATO could provide lessons for Ukraine.
"Right now in the Ukraine public opinion, unfortunately, supporting NATO is very, very low, about 20-25 percent," he said. "They have to make a lot of effort" to overcome that, he added.
Kirkilas said the people of Ukraine have been subjected to years of anti-NATO propaganda.
The Ukrainian defense minister made a similar point in his comments about strengthening public support. He said the government needs to undertake a more vigorous public education effort and address what he called old stereotypes about NATO that he predicted would be "easily broken."
Among the mistaken stereotypes, he said, is that NATO membership would mean the stationing of nuclear weapons on Ukrainian soil.
At his news conference with the Lithuanian president, Rumsfeld was asked whether the United States, as the leading power in NATO, should take responsibility for the anti-NATO sentiment in countries such as Ukraine. "It seems to me that NATO's polices stand on their own," the defense secretary replied.
NATO has been working to build closer ties with Ukraine since last year's "orange revolution" that brought too power pro-Western President Viktor Yushchenko.
But NATO has stopped short of giving Ukraine a date for opening official talks on membership, saying the timetable depends on the pace of reforms to modernize the military, tackle corruption and strengthen democracy.
Yushchenko has made membership in NATO a major goal, but many Ukrainians, particularly in the Russian-speaking east, are less happy about joining their former Cold War foe.
A small group of protesters shouting "NATO Out!" greeted NATO Secretary-General Jaap de Hoop Scheffer in the eastern city Donetsk on Thursday when he led an alliance delegation on a visit to Ukraine.
During the trip, de Hoop Scheffer repeated his promise that NATO's doors will remain open for Ukraine if it completes the necessary reforms. Yushchenko last week expressed hope that membership talks could begin next spring and some Ukrainians are hopeful it could be included when NATO nations are expected to decide on the alliance's next expansion at a summit meeting in 2008.
But de Hoop Scheffer refused to discuss a timeline.