Scientific Time Sharing Corp is planning an initial public offering of 500,000 shares of common stock. The Bethesda firm was started in 1969 and has become the nation's largest supplier of remote computer services based on the most common business-oriented computer language.

In a registration statement filed with the Securities and Exchange Commission, Scientific Time Sharing said the offering price will be about $10 a share.

Half of the stock being offered by a team of investment companies will come from current shareholders and the balance from the company itself. Scientific Time Sharing plans to use about $2.2 million received by selling 250,000 shares to pay off long-term debts incurred in purchases of computer equipment.

Scientific Time Sharing's computer services are designed to meet a broad range of data processing needs based on programs for computers called APL - for A Programming Language, which has been adopted widely in business because it performs all types of analysis and data reporting without requiring the user to have experience in programming for computers.

Programs are designed to handle specific problems or tasks for computer analysis. The Bethesda firm has developed modifications to basic computer programs that are used in financial reporting, insurance actuarial analysis, design of communications networks and other information processing.

Customers of the company use these applications by entering instructions in typewriter terminals in their offices that are connected by telephone communications with Scientific Time Sharing's computer center here. The network now reaches more than 200 cities in North America and Europe.

The SEC registration statement provides a look at Scientific Time Sharing's financial information for the first time. Among developments disclosed to potential investors:

Profits in the year ended last May 31 totaled $1.18 million (81 cents a share) on revenues of $13.6 million. The previous year, the Bethesda firm earned $1 million (72 cents) on sales of $10.2 million.

During the past three years, revenues have grown consistently - from increased use of existing customers and the addition of new ones. Eight divisions of one customer - Citicorp, the New York holding company for the nation's second-largest commercial bank - accounted for 3 percent of revenues in fiscal 1976, 13 percent in fiscal 1977 and 24 percent in fiscal 1978.

Just as Citicorp's business has helped the Bethesda firm expand its business, the New York bank company may cause-Scientific Time Sharing to lose a significant share of business as Citicorp cuts back on use and considers bids from a competitor for similar services this year. Such a revenue loss "could adversely affect" the firm without increased sales to other customers, and steps already are being taken to adjust expenses to offset anticipated losses.

Scientific Time Sharing sells services through 15 domestic and three European offices, and employs 210 persons. Although the Bethesda company's APL service revenues are larger than those of any other service firm, is revenues compromise less than one percent of the current domestic market for remote computing services. Competitors include such giants as Boeing, Computer Sciences Corp., Control Data Corp., Control Data Corp., General Electric Co. and International Business Machines Corp.

Daniel Dyer, 48, was co-founder of Scientific Time Sharing and has been chairman and president from the first day in business. He owns the second-largest block of stock in the firm (11 percent) and earned $105,000 in the year ended May 31. The largest single block is held by Burton Gray, a director since 1970 and former economist at the Center for Naval Analyses; he owns about 21 percent of the 1.36 million shares now outstanding.

The other co-founder is S. Goran Stackig, chief executive of the Stackig, Sanderson & White advertising and marketing firm which he found in 1960. Stacking has been a director since Scientific Time Sharing started.

A number of directors and executive officers plan to sell 92,400 shares during the public sale, with Dyer selling 15,000 and Gray selling 41,000. Current investors paid $716,669 for the stock they own at average prices under $1 a share.

Although Scientific Time Sharing previously has paid no dividends and states that policy is "to retain earnings and use funds for operations and expansion," a successful completion of the public offering would lift a dividend, restriction now existing in connection with bank loans.

The team of investment firms underwriting the initial offering is headed by L. F. Rothschild, Unterberg, Towbin and Alex. Brown & Sons.