Defense Secretary Donald H. Rumsfeld said yesterday that Iraqi security forces are steadily improving, and he dismissed news of a drop in the number of highest-rated units as having minimal relevance.

"There are an awful lot of people chasing the wrong rabbit here, it seems to me," Rumsfeld told reporters, who pressed him and Gen. George W. Casey Jr., the top U.S. commander in Iraq, about the reduction in Iraqi forces considered able to operate independently.

Military commanders revealed the drop during congressional testimony Thursday, saying the number of "Level 1" Iraqi units had declined from three to one over the summer. The disclosure of the normally classified figures drew expressions of concern from some members of the Senate Armed Services Committee, who questioned whether U.S. forces are making sufficient progress in Iraq.

Casey arrived at a Pentagon news conference yesterday armed with statistics intended to show a much-improved Iraqi force. He noted, for instance, that the number of Level 2 units -- that is, those considered able to lead operations with U.S. support -- had doubled since May (up to 36 battalions out of a total 116 army and special police battalions, according to other officials).

Additionally, combined U.S.-Iraqi operations and independent Iraqi actions at the company level or above have jumped from about 100 in May to more than 1,300 now, Casey said. Such operations account for 80 percent of the total, he added.

"The important fact is," said Rumsfeld, ". . . that every day, every week, every month, the Iraqi security forces are larger, they're better equipped, they're better trained and they're more experienced."

He first called the decline in Level 1 units "irrelevant" and then minutes later retracted the remark, saying that "its relevance is minimal" compared with other factors.

Still, while some Iraqi units have improved, others have encountered setbacks. The rating system is based on a range of categories, including manning and equipment levels, logistics, training, leadership, and command and control. Because these conditions can fluctuate, Casey said, the ratings can change -- just as they do for U.S. units under a similar assessment process.

Casey said he did not know the specific reasons for the decline in Level 1 Iraqi forces. He recalled that some adjustments were made in the rating system to make it more understandable after its first run this spring, and some clarifications were provided to U.S. and Iraqi officers making the assessments.

Initially, he said, one brigade and two battalions had been rated in the top category. Now, the single battalion with a Level 1 rating was not even one of the original three units, he said.

The Bush administration has linked any future withdrawal of U.S. forces from Iraq to progress in the development of Iraqi forces. But Casey said "there is not a specific number" of Iraqi units "that have to be capable before we start reducing coalition forces."

Casey reiterated his expectation there will be some reduction in U.S. forces next year.

But he indicated the cut may not be as large as he thought as recently as July, when he predicted a "fairly substantial" withdrawal by next spring.

That prediction, he said, had assumed progress on the political and security fronts. But the draft constitution written this summer -- and to be put to a national vote on Oct. 15 -- has drawn strong Sunni Arab opposition and "didn't come out as the national compact that we thought it was going to be," Casey said.