Stocks were mixed at the close Thursday as portfolio managers made last-minute quarter-end adjustments. The Dow Jones industrial average fell 11.18 to close at 3555.12. Advances, however, led declines, 1129-868, on the New York Stock Exchange. Adjusted volume was 280,989,700 shares. Tick jumped to +605 at the close, probably indicative of end-of-quarter purchasing by portfolio managers. The NASDAQ composite index was down 0.39 to 762.78, but advances topped declines by a wide margin on NASDAQ, 1811-1146, in heavy volume of 305,290,700 shares. GM, the most active Big Board issue, dropped 2 to 41 7/8, a 14-week low. GM of Canada reached a deal with the Canadian Auto Workers union averting a strike. The deal is similar to one the union reached with Chrysler Canada, which GM had said that it did not want to accept as a model. United Airlines' flight attendants dropped out Thursday from the coalition it formed with pilots' and machinists' unions to gain control of the carrier. News of the decision knocked down UAL stock by 3 3/4 to 137 1/4. Expectations of the flight attendants' defection pushed UAL down 3 5/8 on Wednesday. YPF SA was up 1 to 25 3/8 as the third most active issue. Smith Barney Shearson added the Argentine oil and gas concern to its buy list. Western Waste Industries did not trade Thursday after falling 2 points to 17 5/8 Wednesday. The company said it "knows of no reason for its recent stock activity," and still plans on a proposed merger with Browning-Ferris. The Dow open, theoretical intraday high and low: 3561.27; 3583.63; 3528.57. Ricky Harrington, senior vice president and technical analyst at Interstate-Johnson Lane in Charlotte, N.C., said the weak bond prices and quarter-end ``window-dressing'' were ``the two main factors that influenced the market today.'' He added there also was ``a little bit of profit taking in technology stocks,'' following their recent run-up. Although bonds fell more than 1/2 point, several interest-rate sensitive market indicators gained ground. The Dow utility average gained 0.13 to 249.80, and the NASDAQ banking index climbed 7.08 to 698.81. WMX Technologies was down 1 to 30 1/2 and Chemical Waste Management fell 1/4 to 8 1/2. The latter said it would cut 1,200 jobs and incur an after-tax charge of $1.74 a share due to a "revaluation" of its incinerator and fuel blending operations. WMX owns 79% of Chemical Waste Management. Rowan Companies was up 3/4 to 9 1/2. It said that business conditions have improved, mainly due to increased drilling revenues in the Gulf of Mexico. IDB Communications was down 1 to 51. Two shareholders will sell 10.7 million shares in IDB. The company will receive none of the proceeds. USF&G was down 1 7/8 to 14 3/8. Kidder Peabody cut 1993 earnings estimates by 15 cents a share to 50 cents, citing low-yielding investments. California Federal Bank was up 1 5/8 to 15. It hired Smith Barney Shearson to "maximize shareholder value." Lomas Financial was rated "sell" by a brokerage house initiating coverage. The stock was down 1 3/8 to 9. Community Psychiatric was up 1 1/2 to 13 1/2 after a brokerage upgrade. It reported an 80% increase in third-quarter per-share earnings Wednesday.