LOS ANGELES, Oct. 23 — A brother of Pat Tillman, the National Football League player who was killed in combat in Afghanistan after leaving his sports career to serve in the Army, has lashed out at the Iraq war in an essay published online.

The brother, Kevin Tillman, who was in the same Army Ranger unit as Pat Tillman, a corporal who was killed on April 22, 2004, by fire from his fellow soldiers under circumstances that the Pentagon continues to investigate, sharply criticized American political leadership and called the war “an illegal invasion.”

“Somehow the more soldiers that die, the more legitimate the illegal invasion becomes,” Mr. Tillman wrote in the 660-word essay that was posted on Thursday on Truthdig .com, a Web magazine offering news and opinion from a “progressive point of view.”

“Somehow,” Mr. Tillman added, “American leadership, whose only credit is lying to its people and illegally invading a nation, has been allowed to steal the courage, virtue and honor of its soldiers on the ground.”

In what are apparently his most expansive public remarks since the death of his brother at age 27, he also does not spare the American public, which he suggests too often relies on superficial gestures to support the troops instead of holding politicians accountable.

“Somehow back at home, support for the soldiers meant having a 5-year-old kindergartener scribble a picture with crayons and send it overseas or slapping stickers on cars or lobbying Congress for an extra pad in a helmet,” he wrote.

Mr. Tillman ended with a suggestion that the elections on Nov. 7 are an opportunity for people opposed to the war to send a message.

“Luckily this country is still a democracy,” he wrote. “People still have a voice. People can still take action. It can start after Pat’s birthday,” Nov. 6.

Despite Pat Tillman’s fame and the outpouring of emotion after his death, the Tillman family has generally kept a distance from antiwar protesters, though they have often spoken of their efforts to find the truth about what happened. Family members did not answer messages for comment on Kevin Tillman’s posting.

A spokeswoman for the Pat Tillman Foundation in San Jose, Calif., where the Tillmans grew up, said, “It is our understanding that Kevin Tillman is not accepting interview requests.”

Pat Tillman, a safety for the Arizona Cardinals, left the team in spring 2002 to join the Army along with Kevin Tillman, motivated in part by the Sept. 11, 2001, attacks and eventually training as a Ranger. After a stint in Iraq, the brothers were sent to Afghanistan.

Pat Tillman died, the Army eventually concluded, after members of his own unit shot him as they searched for enemy fighters in a canyon in southeastern Afghanistan. An Afghan soldier fighting next to him also died.

Kevin Tillman’s essay was posted as Pentagon investigators close in on the latest of several investigations into the case. Initially, the Army had suggested that enemy fire had killed Pat Tillman. Later, the Army conceded that his comrades had shot him.

Under pressure from the family and members of Congress, the inspector general of the Defense Department and the Army Criminal Investigation Command are examining the actions of members of Mr. Tillman’s unit and the initial investigation.

Daniel Kohns, a spokesman for Representative Michael M. Honda of California, a Democrat from San Jose, who pushed for the investigations, said Pentagon representatives said a month ago that they expected to complete their work by the end of November or early December.

A spokesman for the Pentagon said Monday that the investigations were continuing. He declined to comment on Kevin Tillman’s essay.

Robert Scheer, a liberal syndicated columnist and the editor of Truthdig, based in Santa Monica, Calif., said he had written about the case and had spoken to family members in the past.

Kevin Tillman’s article was not solicited, Mr. Scheer said, and the site agreed to Mr. Tillman’s conditions for posting it. The conditions were that it be posted unchanged aside from grammatical editing, including the headline he had written, “After Pat’s Birthday.”

Mr. Scheer said Mr. Tillman had made it known that, after leaving the military last year, he felt now was time to speak out, with his brother’s birthday approaching. Pat Tillman also had expressed anger about the war to friends, several published reports have said.

“He is not proselytizing, he is not a political person,” Mr. Scheer said of Kevin Tillman. “He just decided because his birthday was coming up he felt strongly that he had to say something.”

Since the article went up on the Web site, it has received more than 4,000 responses, though Web server limits have prohibited publishing that many, Mr. Scheer said.