The Thomson publishing empire intends to press ahead with its effort to acquire the Bureau of National Affairs here by making an offer so attractive that the worker-stockholders would want to accept it despite opposition from BNA's directors.

However, Thomson will not challenge BNA's management in court or pursue a "hostile" takeover, a senior Thomson executive said yesterday.

"We don't make hostile bids," said W. Michael Brown, executive vice president of the Toronto-based International Thomson Organisation Ltd. He said that "all our acquisitions have been made in a friendly way."

BNA, an $85-million-a-year publisher of trade and technical journals, has been owned by its employes since 1947.

Thomson has offered $45 a share for BNA's stock, which is currently valued at $18. The offer applies to both the 900,000 shares of class A stock held by current employes and the 900,000 shares of class B stock owned by retirees, making its total value $81 million, BNA officials said.

The directors of BNA, which has about 1,400 employes, have agreed unanimously to reject Thomson's offer. William Beltz, BNA president, said the company is not interested in being acquired by outsiders at any price, and company counsel Hugh Yarrington said after employes were officially notified of the Thomson approach yesterday that "our position has not changed."

Brown, however, said that Thomson remains interested. "BNA is the sort of company that would fit in with our business," he said. "We are successful, we have extremely high-quality companies, we paid a lot of money for them and we operate in a very decentralized fashion."

Thomson is a worldwide company--based in publishing but also including oil and travel subsidiaries--that had sales of about $2.3 billion last year. Rich with cash from North Sea oil, the company has developed a strategy of using the money to finance "a vigorous policy of acquisition and growth in North America, particularly in the United States," according to its annual report to stockholders.

Thomson's U.S. holdings include Callaghan & Co. and Clark Boardman Co., legal publishers; the Wadsworth group of technical publishers; Medical Economics Inc. and its subsidiary magazines; and the Ward's group of automotive specialty magazines. Many of its publications here, in Canada and in Britain are similar to BNA's lineup of technical newsletters and government reports.

BNA's corporate charter prohibits the sale of stock to outsiders, but the shareholders could vote to amend the charter if enough of them wanted to accept Thomson's offer.

"We have acquired other employe-owned companies," Brown noted.

BNA officials say no negotiations are going on. The next move, if any, is up to Thomson, they said.