I do worry that an ineffective guest worker program (which I think your proposal is) would just convince people that guest worker programs don't work at all. And I do think we need one.
The primary goals of a guest worker program are to make sure that we know who and where immigrants are (your proposal would do nothing toward that); to make sure that they go home after their jobs are done (your proposal would only do that for some); and that they didn't bring dependents with them (your proposal wouldn't stop the ones who want to do that).
And, of course, to make sure that seasonal employers (which many of them are) have the work force that they need, without taxpayers having to foot the bill in the off-season. But why would they care whether they're hiring legals or illegals? The answer is, they don't under the current system, or under your proposal.
All that would be needed would be to combine the program with just a spike in enforcement, and that would be enough to get both employers and employees to see that their best bet is to go the legal route. Once it's jumpstarted that way, it will be much easier to maintain it, because the more people go the legal route, the easier it would be to take action against those who don't.
But if you don't agree, all that would be necessary would be to make it clear at the time the program is enacted that this is a pilot program, and that the option of extending it to illegals, if it doesn't work as fast as some would prefer, will be on the table. But holding it up out of fears that it won't be effective enough will only guarantee stagnancy.