An American Security Bank bond fund in which many Washington pensions plans are invested had the best three-year performance of any bank's bond fund, a national survey reports.

The American Security fund earned a 47.2 per cent return over the three years by actively trading government and corporate bonds.

The fund with average assets of about $36 million, represents pension and profit-sharing investments mostly of local businesses, trade associations and unions, said Eugene W. Mulligan, the American Security trust officer who manages the money.

The fund's performance ranked first in a survey by American Banker, a trade paper, which was released yesterday.

The 47 per cent return was attributed to active trading the use of what bankers call "bond swapping" - selling one bond and buying another to gain a more favorable return.

Mulligan said the fund is limited to fixed-income, non-equity securities.

The portfolio now has 36 per cent of its assets in federal government securities, 37 per cent in corporate securities, 14 per cent in World Bank and foreign bonds and 13 per cent in cash.

Announcement of the fund's performance was one of three developments at American Security.

The bank said it has become a correspondent bank with the Bank of China and launched a new program of rotating top executives into various asignments.

Adopting a management policy common in some industries but rare in banking. American Security assigned Anthony J. D Ermes, senior vice president in charge of personnel, as a general manager of the trust and investment departments. Michael F. Ryan, senior vice president in charge of the treasury division, will become chief personnel officer.