By Matt Spetalnick

WASHINGTON (Reuters) - President Barack Obama
Friday signed into law a $600 million bill to beef up security
on the U.S. border with Mexico, and his aides pressed lawmakers
to set aside election-year politics and work toward broader
immigration reform.

With illegal immigration seen as a key issue in the
November congressional elections, the Obama administration
touted the border enforcement plan as laying the groundwork for
a revived effort to overhaul the U.S. immigration system.

Congress passed the measure this week and sent it to Obama,
who sought the extra funding amid complaints from southwestern
U.S. states that the government was failing to seal the border
from illegal immigrants and drug traffickers.

But lawmakers have been reluctant to push ahead on the
hot-button issue of immigration reform, and no serious progress
is likely until after the mid-term elections.

Obama's aides insisted the president remained committed to
revamping what he has called a broken immigration system, and
challenged Democrats and Republicans to show leadership.

"They will need to address this in a bipartisan way,"
Homeland Security Secretary Janet Napolitano told reporters at
the White House. "It cannot only be done by Democrats. The
Republicans need to come to the table."

But mindful of the political climate, administration
officials set no timetable for breaking the deadlock.

Obama has called for comprehensive reform that includes not
only better border security but a pathway to citizenship for
millions of illegal immigrants. Republican critics support a
tighter border but say citizenship proposals would amount to
an amnesty for lawbreakers.

"If the president takes amnesty off the table and makes a
real commitment to border and interior security, he will find
strong bipartisan support," Senate Republican leader Mitch
McConnell said in a statement.

MORE BORDER PATROL AGENTS

The new $600 million will fund some 1,500 new border patrol
agents, customs inspectors and other law enforcement officials
along the border, as well as two more unmanned aerial "drones"
to monitor border activities.

Congress' speedy approval of the measure marked a rare
display of bipartisanship.

Democratic Senator Charles Schumer said he hoped the bill's
passage would help break the stalemate over broader immigration
reform. Obama, in a statement issued Thursday, said he
wanted to continue working toward that goal.

There are believed to be about 11 million illegal
immigrants in the United States. But immigrants' rights
advocates say Republicans have inflated concerns about illegal
immigrants in order to put Democrats on the defensive ahead of
the Nov. 2 congressional elections.

With the measure's passage, members of Congress running for
re-election will be able to spend the next several weeks
boasting that they acted to reinforce the border.

Officials in southwestern states have asked for more help
from the federal government to stem the flow of illegal
immigrants, weapons and narcotics. Obama already has ordered
more National Guard troops to the border for a year.

A federal judge last month blocked key parts of an Arizona
law that sought to drive illegal immigrants out of the state,
handing a victory to the Obama administration, which argued the
measure was unconstitutional.

The White House also rejected calls by some Republicans in
Congress to alter the 14th amendment of the U.S. Constitution
to eliminate language that gives automatic U.S. citizenship to
all people born in the United States. These Republicans oppose
automatic citizenship for babies of illegal immigrants born in
the United States.

The amendment, ratified in 1868 in the aftermath of the
U.S. Civil War, was intended to guarantee that former slaves
were automatically given U.S. citizenship.

"Those that have, with steadfast fidelity, talked about not
tampering with our Constitution, have now swerved to pick the
14th Amendment as the best place to address comprehensive
immigration reform," White House spokesman Robert Gibbs said.

"It's rich in its irony. It's wrong in its approach."

(Additional reporting by Jeff Mason; Editing by Will
Dunham)