Summer 2007 is just a little more than half over, but studio chiefs are already anxious about their plans for another season of eye-popping tentpoles.

We’re not talking about next summer; we’re talking 2009.

With demands for ever-more-elaborate special effects, the expectation of bigger and better megapic events and the threat of a crippling strike, studios are being forced to plot out their release strategies even farther into the future.

Studios are jockeying to stake their claim to the best prospective dates, clashing into each other in some cases. As things stand, Fox’s James Cameron-directed 3-D “Avatar,” set for May 22, 2009, will go up against DreamWorks “Monsters vs. Aliens,” another 3-D pic.

It doesn’t matter that many theaters are not yet equipped to show 3-D.

And even though “Narnia 2” hasn’t been released, Disney has slated “Narnia 3” for May 1, 2009.

While director Marc Forster is just now working with writers on the next Bond film for 2008, there’s a 2010 date for the one after that.

That 2010 Bond pic exemplifies the latest trend. Many studios, with dates lined up for ’09 and the year after that, have set marketing and merchandising plans in motion and have started talks with visual effects houses. In many cases, the only thing they lack are a director, stars, script or even a story outline.

“As films rely increasingly on CGI, you have to think further and further out, and it’s harder to distinguish from picture to picture, so that puts more pressure on you to get the right date,” says Fox Entertainment president Hutch Parker. “If you don’t, it can really bite you.”

Earlier this year, Disney caused a stir when it disclosed at an investors conference that “Prince of Persia,” produced by Jerry Bruckheimer, would be one of its upcoming tentpoles. Not long after, it announced with much fanfare a release date: July 10, 2009.

The film, based on the bestselling vidgame, has been in development for 3½ years, but there are no actors attached, there is no final script and Michael Bay may direct — but that hasn’t been set, either.

While it’s not unprecedented for studios to stake out dates two and even three years in advance, the practice has become much more pervasive.

All of this advance planning doesn’t necessarily translate into “ready to go.” A firm release date means a firm start date — whether or not a script is ready. On the set of the second and third “Pirates” movies, the joke was, “We’re not shooting a script, we’re filming a release date.”

As much as these movies are planned in advance, it’s a safe bet filmmakers will still be in a rush to finish last-minute tweaks and special effects to meet the release date. It has become the nature of the beast.

Planning is required due to the ambitious technical and marketing demands. But now there’s an even greater impetus to get things moving: the fear of a work stoppage next year.

“Right now, a lot of the decisions are being driven by the strike,” says Universal production president Donna Langley. “It’s requiring studios to frontload what they’re scheduling for production so that you can make sure that you’re in front of that deadline.”

Aside from strike fears, studios want to ward off other studios by planting the flag early. They also need to draw the most talented FX workers and book as many screens as possible.

That screen battle comes with an added twist for Fox’s 3-D “Avatar” and DreamWorks’ 3-D “Monsters vs. Aliens.” The presumption is that many existing screens will be converted to digital in the next few years, and some of those will be made 3-D-ready. But there’s no solid prediction on how many will be available at that point.

There’s also the branding challenge of introducing entirely new sets of characters and stories to audiences. With many franchises having run their course, 2009 is shaping up to be a year with a surprising amount of new fare that will, it is hoped, spawn sequels of their own. There’s not just “Avatar,” “Monsters vs. Aliens” and “Prince of Persia” but Pixar’s “Up” (slated for June 12) and Sony’s “Green Hornet” (expected to get a summer bow).

“These (2009 titles) are all big family-type projects that have a lot of branding and licensing opportunities,” says Rob Friedman, the former vice chairman of Paramount who is now a principal at Summit Entertainment. “That takes a lot of pre-planning; so if you want to avoid being stacked up against another tentpole, it’s always a smart thing to do. You’re going to be working with toy companies, fast-food companies to build long-range awareness.”

What’s more, studios have been scheduling more global day-and-date bows, putting even more pressure to lock down screens in various territories as early as can be.

“You have to get there early, particularly for big dates around Memorial Day and the Fourth of July, and it takes a tremendous amount of work,” says Anthony Marcoly, vice president of sales and marketing for Buena Vista Intl.

“What we’re doing is emphasizing the Disney brand in a wider variety of ways. Our message is that ‘this is not just a teen movie’ or a ‘family film’ but something that is for everyone from 8 to 80 in every country. These are truly global properties.”

Of course, the advance planning carries a risk: To lock into a date is to commit to meeting it. Promotion and marketing partners depend on it.

Sony’s Jeff Blake notes that the dangers of early dating include having to move a film. “Rightly or wrongly, that film can get stigmatized if you move it once or twice because you run the risk of creating the impression that there’s something wrong with the film. At some point, it’s not worth it to get too far ahead of yourself until you’re completely sure of what you’ve got.”

Early dating can also limit a studio’s options. Paramount’s Sherry Lansing was faced with that problem in the summer of 2004 when Joe Carnahan departed “Mission: Impossible 3,” to be replaced by J.J. Abrams. But Abrams wasn’t going to be available to shoot the sequel in time to make the summer 2005 release date. So Lansing had no summer movie until Tom Cruise and Steven Spielberg agreed to do “War of the Worlds” instead.

In other words, the studio had the slot; it just needed to fill it.

“I think dating in advance has led to the expansion of when you can release a tentpole movie,” Blake says. “It used to be that the Thanksgiving weekend was when the holiday season started and now that’s been pushed back to the start of November. And we’ve managed to get summer to start on the first weekend in May.”

With worldwide releases, there are perhaps a dozen weekends a year that will work, mostly between May and July and then again in November and December.

Disney and Fox have been especially aggressive about claiming key weekends.

Disney’s third “Narnia” opens on May 1, 2009, less than a year after the second one opens. It’s signed Michael Apted to direct, with shooting starting in January; Stephen Marcus and Chris McFeely, who wrote the second “Narnia” film, are also writing this project.

“The first one made $745 million, so it’s important for us to keep the train moving quickly because people want to see more,” Marcoly explains.

Six weeks later, on June 12, Pixar’s comedy “Up,” about a geriatric detective, will open. And on July 10, it has slated “Prince of Persia.”

Fox, meanwhile, not only has “Avatar” but “Ice Age 3” slated for July 1. Later in the year, it has “The Fantastic Mr. Fox” on Nov. 6.

“We’ve never been in a time where ‘dating’ has been more critical,” Parker says. “It’s very much an issue for everyone and it’s a deeply intricate challenge.”

Other studios are more circumspect about their plans. Warner Bros. and Universal, for example, haven’t announced any firm dates, but they do have a handful of movies on the slate. While Warner Bros. is weighing various tentpoles like a “Superman Returns” sequel and “Justice League,” execs there say they don’t date films that aren’t greenlit. But they admitted they have “several high-profile possibilities,” including “Watchmen.”

And Universal’s “Nottingham,” starring Russell Crowe, is probably going to wind up with a 2009 release.

“We’ve always presumed that ‘Nottingham’ would be a 2009 film but we would not set a date until our development is a little further along,” Langley notes. “And we’re not in a horse race with the other studios to get our pictures dated before the others. In the case of ‘Prince of Persia,’ I think it may be a question of wanting to keep the momentum going from ‘Pirates of the Caribbean’ plus looking for an optimum release date.”

New Line, for example, has held off on announcing any date for “The Subtle Knife,” the sequel to “The Golden Compass” in the Philip Pullman “His Dark Materials” trilogy. The mini-major won’t even make the decision to go ahead with the second film until after it opens “Compass” in December — though it’s already hired a writer.

Should there be another “Pirates,” there is a natural place for it: 2010. Studios are starting to claim dates on that year as well, and as it stands it is beginning to look a lot like … well, 2007. Currently on the docket are “Spider-Man 4” and “Shrek 4,” along with a “Harry Potter 7.”