(Updates with fresh remarks, changes dateline to Madison)

By Patricia Zengerle

MADISON, Wis. (Reuters) - President Barack
Obama worked Tuesday to portray Republicans as catering to
millionaires over the middle class while trying to energize
young voters ahead of Nov. 2 congressional elections.

"I need you fired up," Obama told a rally at the University
of Wisconsin-Madison. "We need you to stay fired up. Because
there is an election on Nov. 2nd that is going to say a lot
about the future -- your future and the future of our
country."

Obama is on a four-state tour this week looking to drum up
support from young voters who helped send him to the White
House two years ago and who may be crucial in helping Democrats
hold on to their congressional majorities on Nov. 2.

He is visiting New Mexico, Wisconsin, Iowa and Virginia --
all states he won in 2008 and likely will need again in his
expected re-election campaign in 2012.

The message Obama carried at his first event, in a family's
backyard in Albuquerque, was that his Republican opponents want
to extend all Bush-era tax cuts that expire this year, even for
incomes above $250,000 a year.

He continued that theme in Madison, telling a crowd of more
than 26,000 in a hoarse voice, "We cannot sit this one out."

Obama says the end result could be damaging to the middle
class who depend on government assistance to go to college and
other programs. Obama wants to extend the tax cuts only for
less wealthy Americans.

Obama earlier used a question from the sobbing son of a
military veteran -- who said his father was not getting the
care he needs from a Veterans Administration hospital -- to
push his attack.

"This is again an example of where come November we've got
to start making some choices because if for example we give tax
breaks to millionaires and billionaires that cost us $700
billion that we don't have, that money has to come from
somewhere," he said at an event in Albuquerque.

Obama was to spend the night in Des Moines, Iowa, after
headlining the event in Madison.

Obama was so popular in 2008 that musicians wrote him into
songs, movie and television stars flocked to endorse him and
tens of thousands of people turned out for his events.
Republicans derided him as "the world's biggest celebrity."

That momentum carried Democrats to majorities in both the
House and the Senate two years ago.

But support and enthusiasm for Democrats has waned,
dampened by political squabbling with Republicans and an
economy still too weak to reduce the 9.6 percent jobless rate.

"REPUBLICAN BASHING"

"It's in his best interest to bash Republicans as much as
he can and the more he makes this a heated partisan mess, the
less he has to defend the Democrats' failures on the issues for
the last two years," Reince Priebus, chairman of the Republican
Party of Wisconsin, said on a press conference call.

Analysts said Obama was risking his reputation by
campaigning on the road.

"Usually midterms go poorly for first-term presidents and
right now his approval ratings are not good," said Julian
Zelizer, a public policy expert at Princeton University. "This
means the results could be the same in November, and he would
give fodder for a storyline about how he was ineffective."

Obama also appealed to young voters in an interview with
Rolling Stone magazine in which he said it is "inexcusable" for
Democratic voters to stand on the sidelines in the Nov. 2
elections and urged them to shake off their lethargy.

"The idea that we've got a lack of enthusiasm in the
Democratic base, that people are sitting on their hands
complaining, is just irresponsible," Obama said in New Mexico.

The rally in Madison, featuring singer Ben Harper, is to be
the first of a series that organizers hope will generate
enthusiasm reminiscent of 2008. But that could be difficult
with only five weeks before the elections.

Obama's approval ratings have dropped to about 45 percent
in recent months from more than 60 percent 18 months ago.

Republicans, benefiting from the burgeoning conservative
Tea Party movement, have generated far more enthusiasm this
election season than Democrats.

Last week, Republican congressional leaders unveiled a new
"Pledge to America" campaign plan to create jobs, cut taxes and
shrink government, including rolling back Obama's signature
healthcare overhaul.
(Additional reporting by Alister Bull, writing by Steve
Holland; editing by Mohammad Zargham and Bill Trott)