WASHINGTON — Nearly three-fourths of military reservists called to serve in the wars in Afghanistan and Iraq make significantly more money on duty than they did in their civilian jobs, according to a new study on military pay.

Seventy-two percent of Army and Air National Guard and Reserve members deployed in 2002 and 2003 saw a significant increase in earnings, according to the study released Jan. 25 by RAND Corp., a research institute funded by the military. The average boost was $850 a month.

A key reason for the increase was the federal tax exemption and other allowances approved by Congress for the troops, who in many cases earn a higher gross salary in civilian life.

The results of the study run counter to the common belief that Reserve and Guard troops suffer financially when they're called up.

The study is part of an effort to track the effects of the war on terrorism on part-time troops. Since the 9/11 attacks, those troops have been called up by the tens of thousands.

The Army National Guard, heavily used in Iraq, missed its recruiting goals last year. Currently, about 108,000 Guard and Reserve members are on active duty.

News coverage of the National Guard and Reserves often focuses on the financial hardships of the members. In 2004, the Defense Department conducted a survey of reservists, in which more than half said they lost income when they were deployed.

However, the RAND study found that only about one-fourth of reservists suffered a loss in income after being activated. RAND researchers compared Social Security earnings data for service members before they were deployed with Defense Department records afterward.

RAND also surveyed more than 110,000 Army and Air National Guard and Reserve members for the study.

Though the study ends in 2003, the beginning of the U.S. deployment of troops to Iraq, preliminary figures for later deployments show the pattern continues.

Jacob Klerman, a RAND senior economist and co-author of the study, said the study is narrowly focused on earnings and doesn't include the extra expenses that reservists often must pay. Also, he said, more research is needed on the long-term effect that being called to active duty has on the careers of those in the Guard and Reserves.

Some reservists find that their jobs or businesses suffer in the long term because they were gone.

"We are looking here at earnings while people are activated," Klerman said. "That's different than the question about what will happen when (they) get back."