Light sport pilot reports being instructed to taxi to Runway 27 although ATIS was advertising Runway 9; with traffic on downwind for Runway 9. The Tower Controller thought he had issued instructions for Runway 9 but apologized after reviewing the tapes.

Narrative

I intended a short recreational flight from YKM to the foothills about 10 NM northwest and back. I requested taxi for takeoff with ATIS information Golf; VFR departure northwest; 'from Intersection Alpha 3; if available.' Current ATIS advised Runway 9 in use. Ground instructed me to taxi 'to Runway 27; Intersection Alpha 3; via Alpha.' I completed a run-up at A3; switched to Tower frequency; and advised 'Experimental XX ready at Alpha 3.' I deliberately did not specify the runway because there was a light crosswind from the south-southeast; there was an aircraft about to enter a right downwind for Runway 9; and although I had been instructed to Runway 27; I thought the Controller might switch me to Runway 9. On the other hand; I thought he may have given me Runway 27 for an easy transition to a northwest heading. The clearance was 'Experimental XX ; without delay; cleared for takeoff on Runway 27.' I confirmed; 'Experimental XX; cleared for takeoff; Runway 27.' I did not challenge the assignment; even though my gut didn't feel it was correct. In my takeoff climb; just over the numbers; I noticed the other aircraft abeam on a right downwind for Runway 9 and thought; 'This is a mistake.' Immediately; the Controller called; 'Experimental XX; you were cleared for Runway 9; continue on course.' I replied; 'I was given Runway 27; sir.' He instructed me to turn right. It was not a near miss situation; but separation was reducing. When I called for landing instructions about a half hour later the Controller assigned straight in for Runway 9 and said; 'You can call me at the Tower. I owe you an apology.' After I landed; we had a cordial phone conversation; in which the Controller stated they had 'played the tapes' and repeated his apology. My lesson was to trust my gut and challenge (or at least re-confirm) an assignment that doesn't feel right. I think a contributing factor was the added stress on Controllers due to the runway being under construction for a month for repaving; with alternating displaced thresholds and constant equipment and personnel accessing the runway during aircraft operations. I think airport management needs to better address safety issues arising from extended periods of runway disruption. At the time of this event; the last 2;500 FT of Runway 9 was out of service.