Former Army Secretary Thomas E. White said the service was making a mistake by lowering its standards. "I think it's disastrous. You are throwing the towel in on recruiting quality," said White, a retired general whom Defense Secretary Donald H. Rumsfeld fired in 2003 over other policy differences.

"We have clear experience from the 1970s with recruiting a sizable number of people from the lowest mental categories," said White. After the Vietnam War, the Army accepted a higher proportion of low-scoring recruits, leading to training and discipline problems, he added.

To achieve last month's recruiting targets, 12 percent of those accepted by the Army had the lowest acceptable results. They scored between 16 and 30 points out of a possible 99 on an aptitude test that quizzes potential soldiers on general science, mathematics and word knowledge.

No more than 4 percent of all recruits can come from that lowest category, according to Pentagon limits. Army officials insisted they would still meet the 4 percent goal - despite the October spike - when numbers are tallied for an entire year. October is the first month of the service's fiscal year, which will end Sept. 30, 2006.

"We're on track to meet our 4 percent annual goal," said Lt. Col. Brian Hilferty, a spokesman for Army personnel. He declined to comment on the 12 percent figure. "It's very early in the year," he said.

The National Guard's October recruit pool included 6 percent from the lowest-scoring category, though Guard officials also said they expected that figure to drop below the 4 percent ceiling by the time the recruiting year ends. Defense officials discussed the numbers on the condition of anonymity. The recruiting figures will be officially released later this week.

The number of poor-scoring recruits brought in by the Army Reserve, which officials said also achieved its monthly recruiting goal in October, could not be determined.

Charles Moskos, a military sociologist at Northwestern University, said he was concerned that the reduction in the quality standards for military recruiting signaled a return by the Army to the troubled personnel era of the 1970s. He said the military must come up with new ways to attract better recruits.

The Army, which has about 492,000 soldiers, hopes to attract 80,000 recruits in 2006 as part of an effort to increase the size of the force by 30,000 during the next several years. The Army National Guard has a goal of 70,000 recruits over the next year, to maintain its force of 350,000.

Officials blame the recruiting problems on the deadly war in Iraq and an improved economic climate at home, which has made it more difficult to sign up volunteers for military duty.

Army Secretary Francis J. Harvey told reporters last month that the Army would begin accepting more people who scored in the bottom third on the military's aptitude test, increasing the proportion to 4 percent from 2 percent. The Army had kept the figure at 2 percent since 1990.

But Harvey did not say that the Army already had brought in 4 percent - or roughly 2,900 of its 73,000 recruits - from the lowest category for the 2005 recruiting year, which ended Sept. 30. In 2004, the Army accepted just 440 soldiers from the lowest category, or about 0.6 percent of 70,000 recruits.

The National Guard also doubled its number of low-scoring recruits for the 2005 recruiting year, accounting for 4 percent of its 50,219 recruits.

Even with the lower standards, the Army and the National Guard fell short of their 2005 goals. When the annual recruiting cycle ended in September, the active-duty Army was about 7,000 shy of its goal and the Guard fell about 13,000 short.

In the early years of the all-volunteer Army, much larger percentages of low-scoring recruits were admitted - as high as 50 percent in some years.

Congress and successive administrations imposed stricter quality controls. In 1984, 13 percent of the Army's recruits came from the lowest-scoring category. That figure fell to single digits in the late 1980s and has been at 2 percent or below since 1990.

Federal law allows the military to take up to 20 percent annually from the lowest category, though officials insist they will not go above the Pentagon's stricter limit.

Lt. Col. Mike Jones, deputy director of recruiting for the National Guard, said the military's aptitude test was only a "predictor" of how a recruit would perform in uniform. He said the dropout rate - those who leave after basic training and before the end of their three-year enlistment - was actually lower for those scoring at the bottom than it was for those scoring at the top, according to a study of recruits over the past 10 years.

Those in the three highest-scoring segments have a dropout rate of 50.9 percent, compared with 47.4 percent for the lowest-scoring recruits, Jones said. He also said the number of disciplinary problems was roughly the same among soldiers in the two groups, pointing to the study.

But Moskos and other analysts say that with high-tech weapons systems and ever-more-sophisticated equipment, the Army needs higher-aptitude recruits.

Moskos, an Army veteran, said the recruiting problems could prompt the military to turn increasingly to recent immigrants in filling its ranks. Another option: tapping the pool of recent college graduates by offering an enlistment of 15 months, instead of the current three years, an idea Moskos said has been gaining attention among Army generals.

Moskos also said the recruiting woes might pressure Congress and senior military leaders to draw down the number of troops in Iraq.

As a lure for new recruits over the next year, the Army and other services are pushing for higher sign-up bonuses.