GOOD MORNING: Who’s the biggest booster for the success of U’s “Jurassic Park”? Arnold Schwarzenegger — whose “Last Action Hero” from Col opens a week later. I caught up with Arnold yesterday in one of the three mixing rooms at Sony Studios where “Hero” is winding final post-production. Also on hand with exec producer Schwarzenegger were director John McTiernan and producers Neal Nordlinger and Robert Relyea. They were cool and assured me all’s well; McTiernan said the sked, set in February, is only 12 hours behind. He credits “visual effects consultant” Richard Greenberg with no holdups on the grand finale. (McTiernan got the DGA to OK the special screen credit for Greenberg.) McTiernan revealed, in two past pix, he got the always-feared calls from special effects houses. “They’d tell me, ‘We’re having a little problem,’ and then they’d add, ‘It’ll take a month longer than we expected and it’ll cost another million dollars.’ ” But no such problems with Greenberg overseeing the varied post houses. The final reel mixes Sunday and prints will be shipped next Thursday. Half of the movie’s in the can now. They showed me some of the footage in the final reel. It involves spectacular action, animation with “live” action, humor, and a tender scene between Arnold and youngster Austin O’Brien (12). “I’ve never been happier,” beamed Arnold, who will follow his domestic preem appearances with Europe and Japan … He has a July start on “True Lies” for Fox (Universal overseas) with director Jim Cameron, then follows with U’s comedy “Oh Baby,” co-starring Danny De Vito, directed by Ivan Reitman. Arnold’s “pregnant” in this one. Wife Maria Shriver, who is expecting their third child, wings to D.C. Sunday for the 25th anniversary of the death of Robert Kennedy. Although Arnold’s resigned from the President’s Fitness Commission, he will continue his private citizen’s programs for youth fitness, he assures … Andy Vajna’s talking to McTiernan to direct “Die Hard III.”SURE TO BE A SHOWSTOPPER on Sunday’s Tonys (CBS): Agnes De Mille (89) will be brought on stage (via wheelchair) by one of those she taught to dance: Gregory Hines. She accepts the special Tony for Rodgers & Hammerstein’s “Oklahoma!” which played B’way in ’43 — pre-Tonys. De Mille and Hines will then present the Tony for choreography … Gary Smith, who produces the Tonys, with Walter C. Miller directing, is also readying the “Jackson Family Honors” from Atlantic City Dec. 11 on NBC — Michael and Janet and brothers will perform. LaToya is still a ? In early ’94 Smith produces an ABC spec toasting People mag’s 20th anni … Bob Hope’s 90th birthday party at his home coulda been another special — the lawns were converted into a carnival setting with booths, prizes, clowns, etc. Then the 370 guests entered a giant tent where Ronnie Clint and his Chasen’s corps presented a lavish dinner followed by a “Major Bowes Amateur Hour” show featuring Joey Bishop, Jack Carter, Red Buttons, Ann Blyth, Buddy Hackett, Joey Bushkin, Shecky Greene, Don Rickles, Donald O’Connor, Norm Crosby, Buddy Rogers, Dolores Hope, a dog act, Betsey & Maurice and — L.A. Master Chorale and Les Brown’s band. Johnson Edwards Entertainment produced the show m.c.’d by Dennis James. The audience included Presidents Reagan and Ford, Nancy and Betty, Gloria and Jimmy Stewart, General Westmoreland (did a terrif takeoff on Buttons’ “He was there” routine), the Milton Berles, Dorothy Lamour, Jane Russell, Barbara and Marvin Davis, Anne Jeffreys, Cesar Romero, Sid Caesar, Betty White and “the voice of God”– George Burns. IT WAS THE 20TH ANNIVERSARY of the Carl Reiner Pro/Am Celeb Tennis & Golf Tourney at La Costa benefiting the ERAS Center. And this year $ 100,000 was raised. Gloria and Mike Franks again put together the event for ERAS with exec director Barbara Cull and ERAS chairman Paul Zimmerman. Monty Hall exhibited his auctioneering prowess before the show, which included comics Johnny Yune, Marty Rackman, Destiny, Mark Schiff, Bill Kirchenbauer, songs by Gene Barry and Reiner the inimitable m.c. He’s not anxious to see his sexy “All Kinds of Love” (Birch Lane Press) on screen … Universal got added good word for its summer sked with Wednesday p.m.’s Fallbrook Mall screening (95% excellent/very good) of its August release, “Heart and Souls,” Ron Underwood’s romantic comedy/fantasy with Robert Downey Jr., Alfre Woodard, David Paymer and Charles Grodin … Alabama’s in North Myrtle Beach, S.C., this weekend for the bow of their eatery, Alabama Grill, created by Bob Morris (Gladstone’s) and Patrick (Ma Maison) Terrail … Eight press agents from the Pogachefsky and Rachel McCallister praiseries were on Wilshire Boulevard., holding their Rolodexes and cellular phones, as they were evacuated from their offices by fire in their building yesterday. The phone worked — per this item … Ray Evans winged to Salamanca, N.Y., where the landmark theater is renamed “The Ray Evans Seneca Theater.” Of course partner Jay Livingston’s also on hand.