WASHINGTON -- A congressional hearing about head injuries in the National Football League "is not a battle between us and the league," the head of the NFL Players Union said this morning.

But DeMaurice Smith, who took over for the legendary Gene Upshaw in March, acknowledged differences of opinion with the NFL over medical research. The union has formed its own commission to look at how to protect against and care for traumatic brain injuries and has been quicker than the league to embrace research showing long-term ill effects of gridiron collisions.

Mr. Smith held a news conference in advance of tomorrow's hearing before the House Judiciary Committee. He is scheduled to testify, along with NFL Commissioner Roger Goodell, Steelers team neurosurgeon Dr. Joseph Maroon, and several others.

In June 2007, a Judiciary subcommittee heard testimony on care for NFL retirees that mostly dealt with the league's pension and benefits plans. Judiciary Chairman, Rep. John Conyers, D-Mich., intends to focus this hearing specifically on brain injuries --- and on their ramifications in college and high school football as well.

In an e-mailed statement, NFL spokesman Brian McCarthy wrote: "We testified before the committee two years ago on retired player benefits and look forward to further discussing these important matters and reviewing the work we have done to reduce and properly manage concussions and assist our retired players."

Mr. Smith said he has worked with the league to examine brain injuries, but he intends to zealously guard the interests of his players and retirees.

"I can only push us on this side of the table," Mr. Smith said. "And I will push us hard to get this right."

He praised the league for taking measures to protect player safety, including rule changes penalizing more aggressive hits and testing players' baseline brain function to create a comparison if he suffers a big hit.

Evidence is mounting in terms of the effects of head injuries over a career, including from the NFL itself. The league last month released a study it commissioned showing that former players are diagnosed with Alzheimer's and other dementia at much higher rates than the general population, including 19 times higher between age 30 and 49. It was the first time the league acknowledged a connection between its game and the cognitive function of its retirees.

Former Steelers Terry Long and Mike Webster have figured prominently in the debate over the long-term health effects of an NFL career.

Mr. Webster, a Hall-of-Fame center for the Steelers, died in 2002 and suffered from chronic traumatic encephalopathy from repeated head injuries. His family won disability benefits from the NFL after suing the league's pension fund.

Mr. Long, a lineman, committed suicide in 2005 by drinking antifreeze, but the Allegheny County Medical Examiner's office listed head trauma as a contributing factor to the death as a cause of his depression. Dr. Maroon said at the time that such a diagnosis was merely speculative.

The Judiciary Committee is scheduled to hear testimony from 17 witnesses tomorrow, including Dr. Julian Bailes, of West Virginia University, a former team physician for the Steelers, and Merril Hoge, who played fullback for the Steelers from 1987 to 1993.

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