WASHINGTON (AP) — A measure strengthening the federal background check system for gun purchases will be included in the $1.3 trillion government spending bill being negotiated by congressional leaders, aides said Wednesday.

The "Fix NICS" measure would provide funding for states to comply with the existing National Instant Criminal Background Check system and penalize federal agencies that don't comply. The bipartisan measure was approved in the House, but stalled in the Senate amid concerns by some Republicans about restricting gun rights without due process and complaints by Democrats that it does not go far enough to address gun violence.

The giant spending bill also includes money to improve school safety as Congress struggles to respond to the deadly assault on a Florida high school and other shootings. The money will be used to train school officials and law enforcement officers how to identify signs of potential violence and intervene early, install metal detectors and take other steps to "harden" schools to prevent violence.

The House approved the STOP School Violence Act earlier this month, but the measure has not been taken up in the Senate.

Kris Brown, co-president of the Brady Campaign to Prevent Gun Violence, said she and other gun-control advocates would be disappointed if Fix NICS represents the strongest action Congress takes this year on guns.

"It's a tiny, baby step forward," Brown said Wednesday in a conference call with reporters. "We think it's not far enough."

The Brady campaign has urged a three-point plan that includes expansion of background checks to cover gun purchases at gun shows and on the internet; banning new assault weapons and high-capacity magazines; and enabling court-issued restraining orders against people deemed a threat to themselves or others.

The National Rifle Association backs Fix NICS as a way to add transparency and accountability to the background check system, but has pushed harder for a separate bill allowing gun owners to carry concealed weapons across state lines.

Lawmakers also were discussing a provision that would allow the U.S. Centers for Disease Control and Prevention to do research on gun safety. A law adopted in the 1990's blocks such research and prohibits the CDC from engaging in advocacy on issues related to guns.