Communications tower management firm American Tower Corp. said Wednesday it agreed to pay $3.1 billion in stock to acquire rival SpectraSite Inc., a Cary, N.C.-based operator of wireless and broadcast signal towers.

American Tower expects to issue 181 million shares in the transaction, which is expected to close in the second half of 2005, subject to shareholder and regulatory approvals.

Under terms of the agreement, which was unanimously approved by the boards of both companies, SpectraSite shareholders will receive 3.575 shares of American Tower Class A common stock for each common share held. Based on American Tower's May 3 closing stock price, this exchange ratio equals $61.53 per share, a 9.5 percent premium over Tuesday's closing SpectraSite price.

Following the closing, American Tower shareholders will own about 59 percent and SpectraSite shareholders will own about 41 percent of the combined company, which will have a portfolio of more than 22,600 communications sites and annual revenue of more than $1 billion.

SpectraSite, which has about 455 employees, posted 2004 profit of $24.6 million on sales of $355.1 million. The company owns or manages more than 7,500 sites. Its shares rose $3.70, or 6.6 percent, to $59.90 in morning trading on the New York Stock Exchange, near the higher end of their 52-week range of $35.60 to $63.99.

American Tower operates nearly 15,000 broadcast and communications towers in the U.S., Brazil and Mexico. The company has about 726 workers, and reported a loss of $247.5 million on revenue of $706.7 million for fiscal 2004. Its shares, which have traded in a 52-week range of $12.50 to $19.28, fell 19 cents to $17.02 in morning trading on the NYSE.