“The last thing in the world we need is anybody walking around here with AR-15s strapped to their back,” he said. “And the absolute tragedy in Dallas is proof positive that we just cannot allow that to happen. I would really just beg these folks, just leave your guns at home. Come, say whatever it is that you want to say, make whatever point it is that you want to make, but it’s going to be very, very difficult to deal with the R.N.C. as it is.”

He added that officers were already in a “heightened state” because of the passions generated by the presumptive Republican nominee, Donald J. Trump, on both sides and the security challenges as thousands of delegates fill the city.

Eric Pucillo, the vice president of Ohio Carry, a gun rights group based in Kent, Ohio, said he understood Mr. Loomis’s concerns, but stressed that people could not be legally prevented from carrying their guns downtown.

Convention planners and city officials emphasize that they are prepared for the Republican gathering and the crowds it will attract.

The Cleveland police chief said Friday that after the Dallas shootings the city would be changing its security plans but did not go into detail. Dan Williams, a spokesman for Mayor Frank G. Jackson, also declined to describe how Dallas had reshaped the city’s security plans, or whether officials were concerned about the state’s gun laws.

“We are going to follow the law and the law is the law period,” Mr. Williams said. “We believe that we are prepared.”

Meanwhile, some are planning to take their own security forces to Cleveland.

Tim Selaty, director of operations at Citizens for Trump, said his group was paying for private security to bolster the police presence. While Mr. Selaty said people should be allowed to carry guns, his group is banning long weapons from a rally in a park it is hosting on Monday.