A “Dino”-mite opening by Disney’s “Dinosaur” should cut DreamWorks’ “Gladiator” down to size this weekend.

After its two-week box office reign, “Gladiator” should fall prey to Buena Vista/Disney’s opening of its PG-rated computer-animated “Dinosaur” at 3,257 theaters.

Dinosaur’s” 21% first-choice tracking doesn’t really tell the whole story, according to insiders. “It’s just fine, because kids’ movies don’t track,” says one executive.

Estimates by Hollywood handicappers of just how big “Dinosaur” will open range from a cautious $25-35 million to a really exuberant $35-40 million. Making projections even more challenging is the fact that a great many “Dinosaur” tickets will be sold at reduced prices to children.

“‘Lion King‘ did $40.9 million in its opening weekend,” explains one source. “Now, it opened the end of June. Kids were out of school on Friday. If you look at just Saturday and Sunday, ‘Lion King‘ did about $27 million. Could ‘Dinosaur‘ do $27 million Saturday and Sunday? Let’s say it only does $6 million on Friday – that’s still $33 million.

“I was tempted, at first, to say that with kids in school, this movie can’t get to more than $25 million; but that’s not true. This movie can be in the low to mid-$30 millions. I just don’t know if it has the kind of heat and appeal that ‘Lion King‘ had, and because it’s an animated movie, it’s hard to track.”

Even if “Dinosaur” opens at the low end, with $25-30 million, a distributor says, “They should be absolutely thrilled. To me, they’re taking a chance. Disney’s always been very shrewd about going with their animated movies when the kids are available. They go out in late June and at Thanksgiving. They haven’t made the mistake some other companies have, by going in May or in off periods (to avoid competition), and then living to regret it.

“When they put this movie on May 19 on their release schedule, it told me they were willing to take a risk and that they felt they had a movie which would appeal to a wider audience than what’s traditional for animated films. And a movie they thought would play well, that would make it into June when the kids would really be available. So I think it is a bit of a risk. If they come out of this with anything in the mid-$20 millions or higher, going into Memorial Day weekend, when their audience expands, I think they’re looking good.”

Other insiders are predicting “Dinosaur” will set a new record for the year’s biggest opening to date. The current record holder is DreamWorks’ “Gladiator,” with $34.82 million the weekend of May 5-7. “It’ll last about one week,” says one optimist. “‘Gladiator’s’ record only lasted two weeks. Records are made to be broken.”

Directed by Ralph Zondag and Eric Leighton, it features such voices as D.B. Sweeney, Ossie Davis, Joan Plowright, Della Reese and Alfre Woodard.

With “Dinosaur” stomping through the marketplace, DreamWorks’ R-rated action adventure “Gladiator” (half owned by Universal, which is releasing it internationally) should fall one sword to second place in its third week. Its first-choice tracking is still a solid 28%.

With over $75 million already in hand, “Gladiator” is heading for $150 million in domestic theaters.

Directed by Ridley Scott, it stars Russell Crowe.

“If ‘Gladiator’ drops another 30% this weekend, as it did last weekend, it’s in the $17-18 million range,” predicts one studio source. “I think ‘Gladiator’ hangs in there. I think ‘Gladiator’s’ first serious dent comes from ‘Mission: Impossible 2.'”

Paramount’s “Mission 2” – known for shorthand as “M: I-2,” which officially starts Hollywood’s summer season May 24, is already looming as a blockbuster with $200 million potential in domestic theatres.

“It already has a 25% first choice, and most of their TV spots haven’t even run yet,” points out one insider. At this point, it’s a 33% first choice for males and an 18% first choice for females. “It’s got 93% awareness and 13% unaided awareness. Those are big numbers. It’s opening at well over 3,000 theaters.”

“It’s going to be huge,” promises a top executive at another studio.

The original “Mission” set a record as the first film to open at 3,000 theaters when it arrived May 22, 1996, at 3,012 theaters. It grossed $56.81 million in its first five days ($18,862 per theater) and $74.91 million for its first seven days of release. “Mission” went on to gross $180.9 million domestically and $284 million internationally for a worldwide cume of $464.9 million.

M:I-2” is expected to set a new record for opening weekend theaters. Opening at 3,500 theaters would do it, since the present record is 3,467 theaters for Miramax/Dimension’s “Scream 3,” which grossed $34.71 million the weekend of Feb. 4-6, 2000 ($10,013 per theater).

Third place on this weekend’s chart should go to DreamWorks’ R-rated youth appeal comedy “Road Trip,” opening at 2,530 theaters. Its 14% first choice should put it somewhere in the $11-14 million range.

Directed by Todd Philips, it stars Breckin Meyer and Sean William Scott.

DreamWorks could also take fourth place with its opening of Woody Allen’s PG-rated comedy “Small Time Crooks” at 865 theaters. But it’s not likely to do big-time business given its 4% first-choice tracking and somewhat limited release.

“It is, after all, a Woody Allen movie,” reminds one observer, projecting a $4-5 million opening. “No matter how much they try to sell it like it’s ‘old Woody Allen,’ it’s still Woody Allen.”

Written and directed by Allen, it stars him, Tony Darrow, Hugh Grant, George Grizzard, Jon Lovitz, Elaine May, Michael Rapaport, Elaine Stritch and Tracey Ullman.

Warner Bros. and Franchise Pictures’ PG-13 rated sci-fi action adventure “Battlefield Earth” should round out the Top Five. “Earth” opened in second place last week to largely negative reviews. Insiders insist it’s generating unfavorable word-of-mouth and will plunge to a lower second weekend orbit.

“I think it’s going to have a $5 million weekend,” an insider speculates. “It’s going to be down 55-60%. They got it open (to $12 million) in a market with really only one movie as competition (‘Gladiator’) and obviously a big marketing budget and John Travolta’s name, but I don’t think they’re going to get lucky two weekends in a row.”

“It’s not showing up at all (in the tracking),” says another studio source. “It’s going to fall off the face of the earth. Figure at least a 50% drop off.”

Directed by Roger Christian, it stars John Travolta, Barry Pepper and Forest Whitaker.

Saturday night will see Buena Vista/Touchstone hold sneak previews of its PG-13-rated action comedy “Shanghai Noon” at about 1,200 theaters.

Shanghai” opens May 26 – right on the heels of “M: I-2’s” May 24 blast off – at about 2,500 theaters.

Directed by Tom Dey, “Shanghai” stars Jackie Chan, Owen C. Wilson and Lucy Liu.

Universal’s PG-13-rated World War II submarine drama “U-571” should descend three fathoms to sixth place in its fifth week.

“If they’re down 35%, that puts them at $3.7 million. So $3.5-4 million is where they’ll fall,” a distributor says.

Directed by Jonathan Mostow, “U-571” stars Matthew McConaughey, Bill Paxton, Harvey Keitel and Jon Bon Jovi.

Filling out lower rungs: “Flintstones in Viva Rock Vegas,” “Frequency,” “Center Stage” and “Where the Heart Is.”

Lions Gate goes wide this weekend with its R-rated drama “The Big Kahuna,” to about 300 theaters after three weeks of not-so-big business in limited release.

Directed by John Swanbeck, it stars Kevin Spacey, Danny DeVito and Peter Facinelli.

On the limited release front: Miramax Films expands its critic lly-acclaimed, R-rated contemporary version of “Hamlet” into exclusive engagements in seven more top markets following its very encouraging launch last weekend in New York and Los Angeles.

Directed by Michael Almereyda, it stars Ethan Hawke, Kyle MacLachlan, Sam Shepard, Diane Venora, Bill Murray, Liev Schreiber and Julia Stiles.