International Telephone & Telegraph Corp. has reached an agreement to buy Dialcom Inc., a small Silver Spring computer company that specializes in automating offices to make workers more productive. Chief among the company's services is a sophisticated electronic mail system used by U.S. firms and foreign countries.

The acquisition, announced last week by ITT, will place Dialcom into one of ITT's largest operations. It will become part of ITT World Communications Inc., which provides a variety of communications services to link computers, teleprinters, facsimile units and other computer-based terminals domestically and internationally.

"It's a good marriage between the two companies," said Dialcom President Robert Ryan. "Our products complement those of ITT and their offerings complement ours. It's a great opportunity for Dialcom to expand and capitalize on the knowledge of ITT," said Ryan, who will remain as the president and chairman of the board of Dialcom.

The company's offices will remain in Silver Spring where most of its 110 employes are located.

The acquisition price was not made public.

Last year Dialcom had revenues of $8.3 million from about 1,200 customers, including such major firms as Westinghouse, Armco Steel and Chase Manhattan Bank. Another large Dialcom customer is the House of Representatives, where the company has helped automate the offices of 240 members.

Dialcom also has licensing agreements with the British Post Office to develop and market an electric mail system throughout the United Kingdom, and has signed letters of intent for similar agreements with Australia and Hong Kong. The company is now engaged in discussions with countries in Europe, the Middle East and Africa for similar agreements.