In some versions (I believe a2k to be one), compact & repair resets to one, else, if the autonumber field is not used in any relationships, then you can run the following sql (either as a stored query, docmd.runsql, currentdb.execute ...)
ALTER TABLE MyTable ALTER COLUMN MyAutoNumberField COUNTER (1, 1)
But - this indicates you're assigning a business meaning to the Autonumber, which is something seldom recommende. One would usually se recommandations of only using the Autonumber field as means of identifying a record, relationships between tables etc, and hide it to the users.
Agree with RoiyVidar, that implicitly you are deriving a value form the autonumber. Often this happens with invoice / order numbers, where a bean counter / auditor / goverrment extortionist (AKA taxman) needs to se contiguous numbers.
If you have this issue then either you have to generate your own primary key in place of the autonumber function- there are some usefull examples here if the search facility lets you see them. OR you have to provide the document trail to indicate why the missing numbers are not valid invices / orders - effectively you store a flag which indicates if its a live / valid record or transfer the old row to an deleted table. Either way its messy.
Another way to reset the autonumber field is to delete it and then re-create it and all the associated references, which frankly is a pain. Ber in mind that an autonumber field is a system generated number - some database engines allow you to specify the start number, some allow you to specify the interval between numbers. As a system generated number it shouldn't matter what the value is providing you can have confidence that it is unique - its there to help the data storage and retrieval mechanisms not for human (neccesarily) for human usage.