By Simon Evans

(Reuters) - The National Football League's NFC Conference is producing some of the season's most in-form teams and Sunday's clash between the Detroit Lions and San Francisco 49ers will be a stern test for the division leaders.

Elsewhere in the conference, the New Orleans Saints face NFC South rivals the Tampa Bay Buccaneers in Florida where the 2009 Super Bowl winners will be looking to extend their lead atop one of the league's toughest divisions.

While the Super Bowl champion Green Bay Packers remain favorites in the NFC thanks to an impressive 5-0 start to the 2011 campaign, it is the rise of Detroit that has been the story of the season so far.

The NFC North-leading Lions (5-0) relished their nationally televised win over the Chicago Bears Monday while the NFC West-leading 49ers are coming off a crushing 48-3 victory over Tampa Bay that showed the turnaround San Francisco (4-1) has enjoyed under new coach Jim Harbaugh.

A year ago, the 49ers were 0-5 and had a minus-10 turnover differential. This year, they are plus-10 in that category and are third in the league with eight interceptions.

San Francisco's impressive pass rush and smart secondary means Lions quarterback Matthew Stafford will to have to be at his most quick thinking to keep the Detroit offense moving.

"They put pressure on the quarterback and in most of their schemes, all of the guys in the secondary are facing the quarterback," said Stafford.

"They don't play a lot of man coverage where guys are turning their backs so that you can throw it right by their ear and they'll never know. It's guys looking at you and you have got to be cognizant of that."

Stafford will no doubt look again to target wideout Calvin Johnson, who had 130 receiving yards against Chicago, including a superb 73-yard touchdown to open the scoring.

The athletic and imposing Johnson, nicknamed "Megatron," is fifth in the NFL this year with 451 yards receiving and 49ers cornerback Carlos Rogers knows he is in for a busy day.

"Johnson's their guy, they are going to get the ball to him any way they can," said Rogers. "Even if he's not open, they are going to throw it up."

The Saints have won four straight since losing the opening game of the season at Green Bay and enjoyed an easy 31-6 win at Tampa Bay last season.

However, the Buccaneers won the return game in New Orleans of the final weekend of the regular season and quarterback Drew Brees believes the Bucs' heavy loss last week will ensure a hard-fought encounter.

"The fact we're going to their place, that it's a divisional game early in the season and they are coming off a tough loss are reasons why we're going to get their absolute best performance and they're going to be ready for us - but we'll be ready for them," said Brees, who threw three touchdowns in last season's game.

Elsewhere, the New England Patriots (4-1) host the Dallas Cowboys (2-2) while the AFC East-leading Buffalo Bills (4-1) visit the New York Giants (3-2).

Monday night's game pits the New York Jets (2-3), looking to recover from a defeat to the Patriots last week, against the winless Miami Dolphins.

(Editing by Frank Pingue)