Francisco Rodriguez, aka “K-Rod,” has vowed to test his value in the free-agency market at the end of the season.

I know this concept agitates some Angels fans. “How can we go forward without our star closer?”

Well, they can do it quite easily:

By letting someone else sign him to a long and extremely expensive contract … and by promoting, say, Jose Arredondo to closer … and using the money they will have saved on A-Rod to sign an infielder who can hit homers and drive in runs.

I am one of those observers who has been convinced by the sabermetricians (stat geeks) that closers are overrated and often overpaid.

Any fairly competent pitcher ought to be able to get through one inning while retaining a lead as big as three runs — which qualifies you for a save.

K-Rod has 38 saves, a record for any reliever before the All-Star break, and could eclipse Bobby Thigpen’s season record for saves (57) — if the low-scoring Angels continue to play scads of close games yet generally manage to take a lead into the late innings.

First, let’s consider the cost of keeping K-Rod.

The Angels apparently offered him a three-year, $34 million contract before the season. K-Rod declined that. (Instead, he went to arbitration, and lost his case, settling for the Angels’ salary offer of $10 million for the 2008 season, over the $12.5 million he asked.)

Presumably, the price can only go up if Rodriguez winds up with 50-plus saves.

At the moment, the biggest contracts to relief pitchers are:

Mariano Rivera of the Yankees, three years, $45 million;

Joe Nathan of the Twins, four years, $47 million;

And Francisco Cordero of the Reds, four years, $46 million.

Rivera and Nathan are having nice seasons. But each could walk off the mound at any moment (like, say, Takashi Saito did, last week) and be out for the year. Or forever. Rivera, for instance, is 38 and will be 41 when his contract runs out. How much zip will his arm have, at that age? Nathan, meanwhile, is 33 and will be 35 when those three years are up. Seems like a gamble there, too.

Cordero, meanwhile, isn’t earning his keep in the first year of his contract. He is 33, with 19 saves, but five blown saves.

Meanwhile, the Angels already have under their control both Scot Shields (who, admittedly, hasn’t shown brightly as a closer) and the aforementioned Arredondo, who reminds a lot of people of the essentially unhittable K-Rod of 2002. He has 23 strikeouts and a 3-0 record in 24 innings, which indicates a nice arm, and has walked only seven.

Shields or, more likely, Arredondo ought to be able to turn himself into a reasonable facsimile of K-Rod by next spring.

And there is this: K-Rod is on a record pace for saves, but his numbers have been getting slightly softer the past two years.

His ERA in 2007 was 2.81, highest since his first full season (2003), and he blew six of 46 save opportunities. His opponents’ on-base percentage was .299 — a career high.

K-Rod is actually a bit worse across the board in 2008. For the first time in his career, he is on pace to have fewer strikeouts than innings pitched, and his K-to-walks ratio is a career-low 1.58. Following on his previous career low (2007) of 2.65.

He also has three blown saves and is developing a reputation for getting himself out of jams of his own creation. That’s not what you want from a premier closer.

So, let’s review:

We have a veteran and accomplished closer who is piling up an enormous amount of saves, a guy whose cost is going up almost by the day because of that … who at the same time seems a little ticked at the Angels organization … even while he is striking out fewer people and walking more than he has before …

To keep him, the Angels likely are looking at a $40 million layout. For three years. When they have at least two good candidates to step in as closer already on the roster.

I say … let K-Rod go. Let some other brain-dead team lavish an enormous amount of money on a guy with a violent and awkward delivery, whose arm could go “pop” at any moment … and let the signed-through-2010 Scot Shields pitch the ninth, or have the minimum-salary Arredondo give it a try.

It seems reckless to let a proven closer go. It isn’t when he would cost you so much to keep, when you have a substitute already at hand, and when you might do something genuinely useful with the $12 million or so (per year) you’re not spending on Frankie Rodriguez.