WASHINGTON — A plan to extend disability benefits to nearly 100,000 war veterans potentially exposed to Agent Orange on ships off the Vietnam coastline were sidelined Thursday over the ongoing dispute about how to pay for it.

The failure again raises problematic questions for lawmakers about how to balance federal costs with government responsibilities.

Critics noted that on the same day lawmakers offered a massive tax reform measure expected to cost $5.8 trillion over 10 years, they could not find a way to cover a small fraction of that total to help sick veterans.

“We’re absolutely appalled at Congress’ inability to reach bipartisan support to take care of it’s blue water veterans,” said Mike Little, director of legislative affairs at the Association of the United States Navy.

At issue is a change in VA policy 15 years ago that excluded veterans serving on ships off the coast of Vietnam — known as “blue water Navy veterans” — from being included in a class of former servicemembers presumed to be exposed to Agent Orange.

Troops who served on the ground in Vietnam or patrolled inland rivers are given special status, simplifying the process to receive disability benefits.

But the blue water veterans still must prove they were directly exposed to Agent Orange for their illnesses to be labeled as service-connected. In many cases, collecting scientific evidence of the presence of the chemical on or near the ships is impossible, given the decades that have passed.

A House bill to restore that status to the Vietnam War sailors has 317 co-sponsors, more than enough to advance the legislation if it reaches the House floor. But leaders on the House Veterans’ Affairs Committee haven’t moved the legislation there because of disagreements over how to pay for the change — expected to total about $1.1 billion over 10 years.

At a hearing Thursday, Rep. Phil Roe, R-Tennessee. the committee chairman, proposed rounding down veterans’ cost-of-living adjustments to cover the cost. The move would cost individual veterans no more than $12 a year in their benefits, but generate around $2 billion in savings that could be reinvested in other veterans programs.

But veterans groups — and committee Democrats — have opposed the COLA change for a host of veterans proposals.

“It’s bad policy to take from one group of veterans to pay for another,” said Rep. Tim Walz, D-Minnesota, ranking member of the committee. “I think this is the time for us to say, ‘No, this money isn’t coming from other veterans benefits.’”

But Roe said that without a way to pay for the legislation, he can’t advance the measure.

“Using the COLA round-down has only recently become an issue for this committee, and it doesn’t make sense to me when weighed against all the good that can be accomplished for veterans,” he said.

Advocates called the funding spat disheartening, especially given that the country loses about 500 Vietnam veterans every day.

“As Veterans Day approaches, it is terrible to think that partisan politics has intervened to deny coverage to sick and dying veterans,” said retired Navy Cmdr. John Wells, executive director of Military-Veterans Advocacy and a longtime activist on the blue water veterans issue

He believes the COLA round-down is an acceptable compromise to get the benefits problem fixed. AUSN officials said they’re disgusted that some solution can’t be found.

“They have had years to work out the details on this,” Little said. “As of two weeks ago, they knew this bill was going to come to the committee for a markup and instead of trying to work together they used blue water Navy veterans as a pawn in their political game.”

His group is also lobbying VA Secretary David Shulkin to restore the benefits under existing VA authorities. Last month, in a hearing before the committee, Shulkin said he is committed to finding an answer but wants to work with lawmakers instead of acting on his own.

Several pending lawsuits could also force a change as well.

But advocates saw Thursday’s hearing as a chance to jump start the issue. Instead, the problem will drag on past Veterans Day, and possibly into next year.