WASHINGTON, July 9 (Reuters) - President Barack Obama's top priorities -- fixing the U.S. economy, overhauling healthcare and addressing climate change -- are proving to be difficult to handle all at the same time.

Obama has insisted in the past that he had to take on all three ambitious issues at the same time because all three demanded urgent attention and all three were necessary to boost the U.S. economy.

As he traveled this week to Russia, the G8 in Italy and Africa, there was evidence that the three priorities were taking their toll on the U.S. Congress.

* Obama's push for quick action on climate change legislation suffered a setback on Thursday when the U.S. Senate committee leading the drive delayed work until September. Democrats in U.S. coal-producing states worry about the impact of the climate change legislation on their economies. Republicans see the bill as a tax increase for Americans. The postponement came as Obama, at the G8 summit of major industrialized nations in Italy, pushed for progress on a new U.N. climate change treaty ahead of a meeting in Copenhagen in December. It could delay getting a bill to Obama to sign.

* Lawmakers during their summer session are struggling to forge an agreement on overhauling the U.S. healthcare system. Supporters of the overhaul are searching for ways to bring down the plan's price tag of at least $1 trillion and pay for it without raising taxes on the middle class and poor. Some of the U.S. Senate's main players on climate change also are central to the healthcare reform debate in Congress. Most experts believe legislation will ultimately be approved but the details are being heatedly debated.

* Obama's biggest challenge is restoring robust growth to the U.S. economy, and he has drawn criticism from Republicans because a $787 billion economic stimulus plan approved in February has had no obvious impact on the U.S. unemployment rate, which is at 9.5 percent and may go higher. Republican opponents have seized on the statistics as evidence that the Democratic president's stimulus package was misdirected and wasteful. They hope to use the issue to win seats in 2010 Congressional elections. Talk has now turned to whether a second stimulus should be considered to provide money more targeted at infrastructure projects. Analysts doubt the political will exists for a second stimulus. (Writing by Steve Holland, Editing by Howard Goller)