Americans yesterday applauded President Reagan's decision to challenge Muammar Qaddafi's "line of death" in the Gulf of Sidra or worried about its consequences -- or both.

"You don't want to see anybody going to war," said Roger Evans, a rancher in Castle Rock, Colo., a town of 6,000 at the foot of the Rockies. "But when you're dealing with a bully you have to do something after a while. Either you whup him or he's going to get all his friends together and start whupping on you."

"I guess we had to show who's got the power," said waitress Donnelle Bradley, tallying a lunch tab at the B&B Cafe. "We can't let Libya and the Russians think they can control us. But . . . it scares me to think what Qaddafi's going to do next."

Retiree Jim King expressed surprise at reports that the Libyans had fired 12 Soviet-built missiles at U.S. planes and missed. "Are they bad shots, or do the Russians make lousy missiles?" he asked.

"I was just starting to think I could get through college without any trouble like this," said Jeff Wirtzfeld, 19, a student at Arapahoe Community College. "If you're my age, you get pretty uptight when you turn on the TV and see that we're in a battle. I saw that and I said, 'Wooooooo -- am I going to be there?' "

Denver oil-and-gas analyst Amy Reid said administration officials have been unable to prove Qaddafi's link to terrorist acts, "so they wanted to provoke him to do it in plain sight. I just wonder why it has to be us every time to make the point.

"Why isn't any other nation as worried about international water law?" Reid asked. "Are we the only other 5-year-old who can get suckered into this?"

"I think Reagan's great," said Ed Berry, 28, a Chicago ad salesman. "The slightest threat to this country -- and he shows America has backbone, and we need that. Americans feel good about themselves. It's simple -- all you have to do is flex your muscles."

"We should nuke 'em. We could bomb them in an hour," said Harold Word, 35, a bicycle messenger on Chicago's Michigan Avenue who described himself as "a permanent private and a bullet stopper in Vietnam."

"It's absolutely irresponsible for Reagan to be doing this sort of thing. He could actually get us into a war," said Phil Prim, 44, a school bus monitor in Austin, Tex. He was walking to Las Manitas Avenue Cafe at lunchtime when he stopped to read through the glass of a newspaper box about a second round of missile fire in the gulf.

"It's disappointing that it happened, but I was not surprised," said Billy Mangham, a local artist and cafe patron. "I was in the Navy . . . . and I know that kind of mentality. When you got that many toys, every now and then you have got to use them. And that is what they U.S. forces are doing."

"I think he did what he should have done," said Danny Sanders, 33, an unemployed roofer reading want ads at a nearby table. "I don't say that he should jump into a war with them, but he should show them that he is going to only take so much."