If a Roth contribution was made in April of 2000 for the year 2000, and then it turns out the AGI is too high to allow the contribution, can the $2000 contribution plus earnings be recharacterized as a traditional IRA and be transferred to an existing traditional IRA? There is no coverage under another retirement plan so there is no issue as to qualifying for a traditional IRA. It's the earnings I am wondering about.

Sure can. In order to avoid the penalties associated with a failed conversion, "you must move the amount converted (including all earnings from the date of conversion) into a traditional IRA by the due date (including extensions) for your tax return for the year during which you made the conversion to the Roth IRA." The text in quotes was taken from IRS Publication 590.

Hope this helps.