Vincent Jackson is a wanted man.

As the days and weeks of the NFL offseason peel away, the big wide receiver of the San Diego Chargers – about to become an unrestricted free agent on March 13 – is a prize target for many teams around the league.

The Chargers have many needs, however, and though team owner Dean Spanos said recently “we’d like to have Vincent back,” it’s uncertain whether the team can retain him.

If Jackson does hit the open market, the Niners should go after him hard.

Though the crop of free-agent wide receivers may be deep and tantalizing – the Giants’ Mario Manningham, the Chiefs’ Dwayne Bowe, the Saints’ Marques Colston, the Eagles’ DeSean Jackson, the Rams’ Brandon Lloyd, the Patriots’ Wes Welker, the Colts’ Reggie Wayne and the Bills’ Stevie Johnson – Jackson is exactly what the 49ers need.

The 6-foot-5, 230-pound wide receiver is big enough to be a playmaker in the red zone and on third down – two weaknesses of the Niners’ offense in 2011 – with the speed and hands to be a deep threat.

Since being drafted out of Northern Colorado in 2005, Jackson has developed into Philip Rivers’ favorite deep-ball receiver. Jackson had some off-field issues earlier in his career, including a DUI, but the past two seasons he has been trouble-free.

Over the past four seasons – excluding 2010 when he played just five games – Jackson has had three 1,000-yard receiving seasons, a total of 28 TDs and catch totals of 59, 68 and 60. This past season he averaged 18.4 yards per catch and his career average is 17.5.

He makes big plays. With Michael Crabtree on one side, Jackson on the other and Vernon Davis at tight end, the 49ers suddenly would have a dangerous receiving corps.

Should Jackson hit the open market, he’d be a hot commodity. There would be competition for his services. His name has been linked to several teams around the NFL that are looking to upgrade at wideout.

ESPN’s Bill Williamson, in grading the unrestricted free agents in the AFC West, ranks Jackson No. 1.

“Receivers with Jackson’s size, speed and skills are rare,” he wrote. “The Chargers want him back but there will be competition.”

Rivers has lobbied for the Chargers to bring Jackson back. He knows the San Diego offense would miss him.

“I want Jackson here,” Rivers told season ticket holders in a conference call this week. “Vincent and I have been together for a long time and we have a great relationship. He is super valuable to us.”

If the Chargers let Jackson get away, however, the Niners shouldn’t waste any time to make him an offer he can’t refuse.

Jackson would be super valuable to the Niners, too.