Can I set JGP compression choice in "save as" dialogue to be "baseline optimized" by default?

It is also possible to preset using actions. If the action is created to a save location that is no longer valid, then that part of the action becomes "generic" alowing one to save to an alternate location while keeping all other recorded properties by default.

Thanks Sebastion - simply use spacebar to select a radio button! I see radio buttons so rarely the key slipped my mind, perfect solution, easy. Thanks again.

You can indirectly. You can use this script which will always bring up baseline optimized. You can also set the quality to what you want. Right now it's on 8. Create an action and record running the script. Then you can assign a hotkey to run it quickly.

var doc = activeDocument;
var f = new File('~/desktop/'+ doc.name)

var idsave = charIDToTypeID( "save" );
    var desc9 = new ActionDescriptor();
    var idAs = charIDToTypeID( "As  " );
        var desc10 = new ActionDescriptor();
        var idEQlt = charIDToTypeID( "EQlt" );
        desc10.putInteger( idEQlt, 8 );//change quality
        var idOptm = charIDToTypeID( "Optm" );
        desc10.putBoolean( idOptm, true );
        var idMttC = charIDToTypeID( "MttC" );
        var idMttC = charIDToTypeID( "MttC" );
        var idNone = charIDToTypeID( "None" );
        desc10.putEnumerated( idMttC, idMttC, idNone );
    var idJPEG = charIDToTypeID( "JPEG" );
    desc9.putObject( idAs, idJPEG, desc10 );
    var idIn = charIDToTypeID( "In  " );
    desc9.putPath( idIn, new File( f) );
    var idDocI = charIDToTypeID( "DocI" );
    desc9.putInteger( idDocI, 248 );
    var idCpy = charIDToTypeID( "Cpy " );
    desc9.putBoolean( idCpy, true );
    var idsaveStage = stringIDToTypeID( "saveStage" );
    var idsaveStageType = stringIDToTypeID( "saveStageType" );
    var idsaveSucceeded = stringIDToTypeID( "saveSucceeded" );
    desc9.putEnumerated( idsaveStage, idsaveStageType, idsaveSucceeded );
executeAction( idsave, desc9, DialogModes.ALL );
app.displayDialogs = DialogModes.NO;