May 25 (Bloomberg) -- Democratic presidential candidate Barack Obama, responding to criticism from John McCain about his lack of military service, said he has no intention of ceding veterans' issues to the presumptive Republican nominee.

``I've said before I respect John McCain's service to our country,'' Illinois Senator Obama told reporters on his campaign plane yesterday. ``But I think the notion that somehow I can't speak out on the behalf of veterans because of the fact I haven't served makes no sense whatsoever.''

McCain and Obama have been trading barbs over military matters. Obama continues to attack McCain's opposition to a Democratic-led measure that would expand the G.I. bill to ensure full college scholarships for people who spend three years in the armed forces. McCain, 71, who spent almost six years as a Vietnam prisoner of war, says Obama has no grounds to criticize because he never served.

Obama, 46, said he was too young to have been drafted or enlist during the Vietnam War.

``But I revere our soldiers and want to make sure that they are being treated with honor and respect,'' Obama said.

Yesterday while campaigning in the U.S. territory of Puerto Rico, which holds its Democratic primary on June 1, Obama told veterans that McCain's opposition to updating the original G.I. bill puts him in the same camp as President George W. Bush.

More Affordable

``I don't understand why John McCain would side with George Bush and oppose our plan to make college more affordable for our veterans,'' he said, vowing not to drop the issue.

``I will continue to fight in the months to come to give those who have defended America the chance to achieve its dream,'' he said.

McCain is against the measure over concern it would encourage too many people to leave the military after just three years. McCain and other Republican lawmakers have proposed legislation that would boost benefits in line with how long a veteran had served.

Obama yesterday also drew differences between himself and McCain on their approach to dealing with climate change. Earlier this month, McCain said he had the superior record on the issue. Both candidates have proposed a carbon emissions trading program to help reduce global warming pollution.

Cap and Trade

``My cap-and-trade system is more aggressive than his,'' Obama said. He also criticized the Arizona lawmaker for not supporting tighter fuel efficiency standards on cars.

Obama also said high gas prices are causing more Americans to change their habits, including buying as many sport utility vehicles.

``People are changing behavior,'' he said. ``We've seen a slump in the sales of SUVs and big trucks and a drastic spike in cars both medium size and small.''

Separately, Obama said he didn't believe McCain's age should be a campaign issue.

``Senator McCain is healthy. He is campaigning actively all across the country,'' Obama said. ``His doctors have given him a clean bill of health. I don't think it should be an issue in the campaign.''

To contact the reporter on this story: Kim Chipman traveling with the Obama campaign, at 1927 or kchipman@bloomberg.net.

Last Updated: May 25, 2008 14:06 EDT