THE alliance between IBM and Apple Computer might be regarded as a kind of "new world order" in the currently agitated US small computer industry. The two high-tech giants announced last week they would join forces to create a new operating system for workstation and personal computers and software for that system.For those who know less about how computers work than how to work them, an operating system is a computer's underlying framework or foundation - the system that tells the machine how to "read" the software it is programmed with. The IBM-Apple alliance, if successful, will force out of the computer field many smaller companies now struggling to stay afloat. The deal may capture the future of small computer use in the US by offering a standardized IBM-Apple system. Currently, the small computer field is split between IBM and Apple systems, which aren't compatible. One standard for PCs would doubtless be a boon. In 1991, one can argue, personal computers have become akin to a utility, like telephones. They ought to be able to "talk" to each other. Yet 4.9 million Apple computers and 16.9 IBM computers can't, whereas co-produced systems could. Consumers, however, will have some questions: Will old systems such as MS-DOS work with the new? And will the new systems eventually require new hardware? Some buyers may delay their purchases to see how the computer landscape sorts itself out. Analysts have doubts about how well the IBM-Apple marriage will work, given the two firms' widely divergent styles of management. But the deal was under negotiation for a long time, and both companies - whose fortunes have been sliding - have a big stake in its success. For now, only one thing is certain: Alliances among once fiercely independent computer firms are the order of the day. The IBM-Apple megapact has infused new excitement, and a vision of sales to come, into a sagging industry.