(Updates with quotes, background on Egypt and Syria)
By Roberta Rampton and Jeff Mason
WASHINGTON/AUBURN, N.Y., Aug 23 (Reuters) - President Barack Obama said in an interview aired on Friday that an apparent poison gas attack in Syria this week was "clearly a big event" but said the United States must be cautious in its response.
In his first public comments since Wednesday's attack in the Damascus suburbs, Obama stressed the importance of international law in responding to the incident, and said he was wary of the financial and human costs of getting involved in complex foreign disputes.
"What we've seen indicates that this is clearly a big event, of grave concern," Obama said in an interview with CNN.
But when pressed about his year-ago comment that chemical weapons use in Syria would be a "red line," Obama expressed caution.
"If the U.S. goes in and attacks another country without a U.N. mandate and without clear evidence that can be presented, then there are questions in terms of whether international law supports it, do we have the coalition to make it work, and, you know, those are considerations that we have to take into account," Obama said.
"The notion that the U.S. can somehow solve what is a sectarian complex problem inside of Syria sometimes is overstated," he said.
Obama called on President Bashar al-Assad to allow a full investigation by United Nations inspectors, but admitted he did not expect that cooperation.
Syrian activists say they are smuggling out body tissue samples from victims of an alleged chemical weapons attack outside Damascus and are trying to get them to a team of United Nations inspectors staying in a hotel a few miles (kilometres) away.
Obama said it would be "very troublesome" if there is proof of a chemical weapons attack.
"That starts getting to some core national interests that the United States has, both in terms of us making sure that weapons of mass destruction are not proliferating, as well as needing to protect our allies, our bases in the region. This is something that is going to require America's attention and hopefully the entire international community's attention," he said.
EGYPT: NOT 'BUSINESS AS USUAL'
In another critical area of the region, Obama said a U.S. decision to cut off aid to Egypt may not influence the actions of the military rulers there.
Obama has come under pressure from some lawmakers to halt aid to the country after the military's violent crackdown there on supporters of ousted President Mohamed Mursi.
"The aid itself may not reverse what the interim government does. But I think what most Americans would say is that we have to be very careful about being seen as aiding and abetting actions that we think run contrary to our values and our ideals," Obama said.
Obama noted that the United States was re-evaluating its relationship with Egypt.
"There's no doubt that we can't return to business as usual, given what's happened," he said.
Asked by CNN whether the time frame had narrowed for decisions on both Egypt and Syria, Obama said "yes." (Reporting by Roberta Rampton and Jeff Mason; Editing by Vicki Allen)