One of the blemishes on Mike Smith’s tenure as coach of the Falcons has been the defense’s inability to mount a feared pass rush.

The Falcons have ranked 25th (2013), 27th (2012), 25th (2011), 25th (2010), 27th (2009) and 17th (2008) in sacks per pass attempt under Smith, while winning two division titles and going to the NFC title game after the 2012 season.

With the Falcons holding the sixth pick in the NFL draft, which is set for May 8-10, the front office could address their pass rush by trading up to select South Carolina defensive end Jadeveon Clowney, widely considered the top player available in the draft.

The Falcons had Clowney in for a visit Wednesday.

“He’s a once-in-every-20-years guy,” ESPN draft analyst Mel Kiper Jr said.

The knock on Clowney is that he put forth an inconsistent effort last season for the Gamecocks.

“I don’t see what other people are seeing,” Kiper said. “I also don’t see any defensive end in the last 20 years that’s been blocked by three guys on a regular basis. That’s because he’s great.”

Smith knows the pass rush must improve, even though he contends that sacks are an overrated stat.

“That’s a function of many things, one being affecting the quarterback,” said Smith, who factors in hits and hurries in addition to sacks in his affecting-the-quarterback equation.

“I say it all of the time, we have to do a better job of affecting the quarterback. You can’t address every issue that you have as an organization in one fell swoop. That’s why there is free agency. That’s why there is the draft.”

In six previous drafts under general manager Thomas Dimitroff, the Falcons made three key first-round trades. They traded into the first round in 2008 to land left tackle Sam Baker. In 2011, they moved up 21 spots and gave up five picks to land wide receiver Julio Jones sixth overall.

Last season, in need of secondary help, they traded up to select cornerback Desmond Trufant.

However, the cost of moving up five spots to land Clowney may be prohibitive for the Falcons, who have other glaring needs along the offensive line, at linebacker, at tight end and at free safety.

To move up, the Falcons would have to give up the sixth pick, their second-rounder, a first-rounder next year and perhaps a fourth-rounder next year, Kiper projected. It’s a steep price, but if Clowney is a once-in-a-generation pass rusher, the team may deem him worth it.

“It costs a lot to go up from six to one because you’re going to get the best player and best defensive end in the last 20 years in Clowney,” Kiper said. “That’s what they need.”

Clowney is a 6-foot-6, 266-pounder who was chosen first-team All-American in his final two seasons at South Carolina. He had 13 sacks as a sophomore and three as a junior, when he appeared to take some plays off.

“I didn’t see the lack of hustle,” Kiper said. “I didn’t see the lack of effort. I saw a guy who played hard 90 percent of the time.”

The other 10 percent of the time, Clowney was away from the play and not required to chase, Kiper contended.

“He is the No. 1 pick,” Kiper said. “Whether he’s with the Houston Texans or somebody else. I’m not taking anybody over Clowney.”

While everyone can see Clowney’s physical gifts, NFL teams don’t know how to project his professional mentality. Will he continue to work hard after signing a lucrative contract? How will he respond to defensive line coach Bryan Cox when he’s ordered to do up-downs after blowing an assignment? Can he make it on time for position meetings?

To help them work through those questions, NFL teams have talked to his high school and college coaches — and others.

“Other people that have had associations with him — former teammates, so forth, so on,” New England coach Bill Belichick said. “It’s a mosaic composed of a lot of different pieces. You try to fit them all together and put some type of valuation on the player.”

With hard-working and serious-minded veteran defensive linemen Osi Umenyiora and Jonathan Babineaux, the Falcons may feel Clowney would have some good mentors.

If the Falcons don’t make a major move for Clowney, there are other viable pass-rushing options later in the draft.

Auburn’s Dee Ford, Boise State’s Demarcus Lawrence, Missouri’s Kony Ealy, Georgia Tech’s Jeremiah Attaochu, Louisville’s Marcus Smith, Arkansas’ Chris Smith and Boise State’s Kyle Van Noy all have been heavily scouted by the Falcons.

“Demarcus Lawrence at Boise State is an underrated player,” Kiper said. “He can get after the quarterback. You may see him in the second-round area. … There are a lot of second-rounders who can get after the quarterback.”

Also, Arizona State’s Carl Bradford or North Carolina’s Kareem Martin also could be intriguing.

“He’s a guy who can help you off the edge,” Kiper said of Bradford. “He can really do some things from a mobility and athletic standpoint.”

In the past two drafts, the Falcons selected defensive ends Jonathan Massaquoi, Malliciah Goodman and Stansly Maponga.

“We’ve got some young guys, though, that I’m very excited about,” Smith said. “Jonathan Massaquoi continues to develop. He’s going into his third season. He has a very good understanding of what it takes to be a successful pass rusher. Stansly Maponga, we feel very good about him as well.”