NEW YORK, NY, June 25 -- Metromedia Fiber Network Inc. has agreed to acquire AboveNet Communications Inc., a supplier of managed Internet services, in a stock swap worth about $1.55 billion. Under the terms of the acquisition, which is expected to be completed in the third quarter of 1999, Metromedia will issue 1.175 shares for each of AboveNet's 31.1 million outstanding common shares.Metromedia is a high-bandwidth fiber optic infrastructure provider. Following the completion of this deal, AboveNet will have access to Metromedia Fiber's planned network of over 1.1 million fiber miles in North America and Europe. By combining Metromedia Fiber Network's virtually unlimited, pure photonic fiber network with AboveNet's high performance connectivity solutions, Internet traffic is able to flow more predictably, far more reliably and at far lower costs, Metromedia Fiber said in a statement. The acquisition is subject to approval by shareholders of both companies and to customary closing conditions.