Skandia Insurance Co. Ltd., a Swedish-based worldwide insurance organization, has acquired 5.4 percent of the common stock of Avemco Corp., a national aviation and financial services firm based in Bethesda, Avemco announced yesterday.

Avemco said Skandia had filed a statement with the Securities and Exchange Commission stating that, as of March 4, it had acquired 136,400 shares of Avemco's voting stock at an aggregate cost of $1.6 million.

Skandia told the SEC that the shares were acquired for investment purposes, and that it currently intends to boost its stake to 15 percent through open-market purchases. The Stockholm-based company already has obtained approval of the appropriate Swedish authorities for its stock purchases.

Avemco, traditionally an insurer of pilots and aircraft in the private-aircraft sector--called general aviation--recently has begun to move into the airline area, starting off by insuring the lenders' interest in aircraft that have been leased to airlines.

Avemco President William P. Condon said yesterday that the company isn't concerned about the Swedish firm's interest. "The indications we've had are that the purchases are for investment purposes only," he said. "We believe that." In its 13D filing with the SEC, Scandia said that it has no present plans or proposals that would result in any extraordinary corporate transactions involving Avemco or its subsidiaries.