WASHINGTON - Legal challenges have stalled the U.S. Food and Drug Administration's proposal to require that graphic warning labels cover half of all cigarette packages, but a new study suggests a less in-your-face tactic - requiring packaging to be plain - might nudge some smokers toward quitting.

Australia was the testing ground for packaging changes aimed at driving down smoking rates. Starting in December 2012, the front of all cigarette packages sold Down Under were to be three-quarters covered with a graphic health warning, and otherwise to be in plain-brown wrap. The brand name and variant was to be displayed in standard size and font, with none of the distinctive markings that set brands apart from one another.

No more classic camel. No more menthol-green stripes. No more Marlboro in typeface so distinctive they named the font after the cigarette brand.

In a study published Monday in the journal BMJ Open, researchers took advantage of the Australian policy's lead-in period to gauge whether the new packaging elicited different responses from smokers than the traditional branded packaging to which smokers had grown accustomed.

In October and November of 2012, the plain new packs - with graphic warnings in coverage that grew from 30 percent of packaging to 75 percent - began appearing in stores.

During November and early December 2012, those conducting the survey contacted 4,004 smokers from the Australian province of Victoria by phone and asked them to rate their cigarettes and smoking experience on a number of dimensions in comparison to those of a year earlier. The questions were embedded in a 12-minute survey purportedly gauging attitudes and behaviors related to smoking.

While 57 percent of respondents were smoking cigarettes bearing the plain-brown wrapper in the first week of surveying, 85 percent were smoking from such packs during the final two weeks as the Australian initiative took legal effect.

Compared with those continuing to smoke from branded packages, respondents smoking from the plain-brown packaging rated their cigarettes, as well as their satisfaction in smoking those cigarettes, less highly than they believed they would have a year earlier. That shift became less pronounced as more and more smokers shifted to the new plain-brown packaging, but smokers' loss of satisfaction with their cigarettes continued to the end of the survey.

Asked about their thoughts on quitting smoking, the plain-pack smokers reported they had thought about quitting more in the past week than had those smoking from branded packs. They also rated quitting a higher priority than did those still clutching their cigarettes in colorful packages.