Further proof that the long-running battle to buy Conrail has become a potential bonanza for lobbyists surfaced over the weekend, with a $460,000 proposal from a public relations firm to "construct a coalition of interests opposed to the private sale of Conrail to the Norfolk Southern Corp."

Jack Bonner, president of Bonner and Associates, said he has no clients in the Conrail battle and that his services have not been solicited by anyone. Bonner is a former press secretary and senior political aide to Sen. John Heinz (R-Pa.), who is "four-square in favor of a public offering" of Conrail's stock, according to his press office.

However, Bonner and Associates has prepared a 48-page document outlining a campaign to build a coalition of labor unions, shippers, politicians, other railroads and ordinary taxpayers opposed to a Norfolk Southern bid to acquire federally owned Conrail, which Transportation Secretary Elizabeth Hanford Dole has vowed to sell.

"Winning the Battle on the Sale of Conrail," as the document is called, was designed to sell his product, and was not in response to someone's invitation, Bonner said yesterday. "There have been some significant nibbles," he said.

The document outlines a number of things that have already happened in the long-running Conrail sales effort.

It suggests creation of a coalition; Heinz has organized a Conrail Coalition in Congress, which his office describes as more of an information-sharing operation than an advocacy group.

The document suggests that the person "out-front" should not be directly connected with a particular company. "Otherwise interviews may become . . . a discussion of a company's vested interest in opposing the sale." Conrail Chairman L. Stanley Crane, who has been personally active on Capitol Hill and elsewhere opposing Dole's plans, has been unavailable to the press for months.

The document promises that, in addition to building coalitions, Bonner can trigger strong mail campaigns with its computers and phone banks and effectively work Capitol Hill. "To insure the member of Congress stays honest, face-to-face meetings in the home district or state will be arranged and we will insure a large number of the faithful turn out to emphasize their support for a public sale," the document said.

That sentence was a slip, according to David Umansky, who works with Bonner and who is a former public affairs chief at the Federal Railroad Administration. "We are not supporting another specific action, such as a public sale. That is just bad editing on a fast job," he said.

The coalition, Bonner and Umansky stressed, would only be against something -- Norfolk Southern -- not in favor of anything. The other bidders still in the running for Dole's endorsement are Alleghany Corp., a New York holding company, and an investment group headed by J. W. (Bill) Marriott Jr. Norfolk Southern has been regarded as the front runner for several weeks.

Heinz' office, Conrail and CSX Corp., a Norfolk Southern competitor that has promised to fight a Norfolk Southern takeover of Conrail "in every forum where the challenge can be brought," all denied that they were instrumental in the document's construction.