I have no survey data to back up my impression that this is typically a BrE-AmE difference. Perhaps I ought to include it in my next pronunciation preference survey. Dictionaries tend to imply that both stressings are found on both sides of the Atlantic. Here’s the on-line OED:The only other familiar adjectives ending in -etive seem to be secretive and interpretive, which follow the stressing of the stem, ˈsecret or inˈterpret respectively, i.e. are stressed on the antepenultimate. There’s also suppletive, a term probably known only to grammarians, which I think most people on both sides of the Atlantic pronounce with penultimate stress, səˈpliːtɪv (the OED has an improbable sʌ- for the first syllable). This reflects the stress pattern of supˈpletion. However in LPD I do also give a variant with initial stress, though I really don’t know to what extent, if any, it is in use.
Words ending in -ative are notoriously idiosyncratic. The best I could manage in LPD was this.
In words of three syllables, the first receives the stress, and the suffix vowel is weak (ˈfricative, ˈvocative, ˈlaxative, ˈnarrative; exception creˈative). In longer words, the stress usually falls on the same syllable as in the underlying stem: acˈcusative, conˈsultative, preˈservative; ˈoperative, ˈqualitative, agˈglutinative, ˌarguˈmentative; adˈministrative. There is sometimes a vowel change (deˈrive — deˈrivative), and there are several exceptional cases (comˈbine —ˈcombinative, ˈalternate — alˈternative, inˈterrogate —ˌinterˈrogative, ˈdemonstrate — deˈmonstrative). Where the primary stress is on the last syllable of the stem, the suffix has a reduced vowel (ˌinterˈrogative); but otherwise in these longer words (ˈcumulative, ˈlegislative) the choice between weak-vowelled ət ɪv ǁ ət̬ ɪv and strong-vowelled eɪt ɪv ǁ eɪt̬ ɪv depends partly on social or regional factors, with British English RP tending to prefer ət ɪv, American English eɪt̬ ɪv: see individual entries.
Those in -itive, on the other hand, are straightforward. They are stressed on the antepenultimate, eg comˈpetitive, deˈfinitive, proˈhibitive, ˈsensitive, ˈpositive, inˈtuitive. I am tempted to say the same about those in -utive. We can certainly agree on conˈsecutive, eˈxecutive, diˈminutive. I think most people also say conˈstitutive, though there may be some who go for ˈconstitutive following the model of ˈconstitute. What about attributive, contributive, distributive, retributive? I use antepenultimate stress in these, but then I also stress the -trib- in conˈtribute, disˈtribute. I wonder about those many Brits who prefer initial stress in these two words. How many of them carry that over into ˈcontributive, ˈdistributive?