Paul, of Kentucky, "does not know what he's talking about, and ... is really spreading fear among the American people," King, of New York, told Fox News.
Both men have said they are considering a campaign for the Republican presidential nomination in 2016.
Earlier Sunday, the libertarian-leaning Paul, who turns 51 Tuesday, defended his planned class-action lawsuit against the NSA over its domestic data-collection policies. He also suggested to ABC's "This Week" National Intelligence Director James Clapper and NSA secrets leaker Edward Snowden deserved to be in the same cell together.
"I think the idea of a class-action lawsuit with hundreds of thousands of participants really beats home and brings to the forefront the idea that this is a generalized warrant and it should be considered unconstitutional," Paul said.
Paul's 2016 campaign website calls for "10 million Americans" to join the lawsuit "to stop Barack Obama's NSA from snooping on the American people" and asks people to donate money to the cause.
Paul also told the ABC program Snowden deserved to be imprisoned for leaking espionage secrets and Clapper should be in the same cell with him for allegedly perjuring himself in testimony before Congress.
Clapper lied in public testimony at an open congressional hearing March 12, 2012, after being asked by Sen. Ron Wyden, D-Ore., if the NSA collects "any type of data at all on millions or hundreds of millions of Americans."
"No sir," Clapper said, then added: "Not wittingly. There are cases where they could inadvertently, perhaps, collect, but not wittingly."
Clapper formally corrected the record June 21, after Snowden's initial disclosures prompted weeks of intense public pressure.
Clapper told NBC News June 9 he thought, "in retrospect," Wyden's question was akin to asking him when he was going to stop beating his wife, which he said was "not answerable, necessarily, by a simple yes or no."
"So I responded in what I thought was the most truthful, or least untruthful manner, by saying no," Clapper told the network.
His formal letter to the Senate Intelligence Committee acknowledged his answer March 12 was incorrect.
"I have thought long and hard to re-create what went through my mind at the time," Clapper said in the letter. "My response was clearly erroneous -- for which I apologize."
"I don't think we can selectively apply the law," Paul told the ABC News program Sunday. "So James Clapper did break a law and there is a prison sentence for that. So did Edward Snowden."
Paul added, "Maybe if they served in a prison cell together, we'd become further enlightened as a country over what we should and shouldn't do."
King, former House Homeland Security committee chairman, told Fox News: "To me, either he's totally uninformed or he's part of that hate America crowd that I thought left us in the 1960s.
"In any event, he doesn't deserve to be in the United States Senate for spreading that type of misperception and absolute lies to be honest with you," he said.
King, 69, a staunch NSA defender, said the spy agency was "doing exactly what it's supposed to be doing."