Sears, Roebuck & Co. has purchased a cluster of historic buildings on Pennsylvania Avenue NW and will make them the headquarters of a new international trading subsidiary.

The Pennsylvania Avenue buildings that once housed the studio of Civil War photographer Mathew Brady will become the base for a new Sears venture to compete in international trade with the powerful Japanese trading companies.

Sears is expected to announce plans Monday to make Washington the headquarters of Sears World Trade Inc., which is headed by Roderick Hills, former chairman of the Securities and Exchange Commission, and Frank V. Carlucci, who resigned last year as deputy secretary of defense.

Sears, the world's largest retailer, has its corporate headquarters and most of its operations in Chicago in the Sears Tower, the world's tallest building. The new trading company and Sears' Washington lobbying operations will be based in a five-story complex now being renovated at 7th Street and Pennsylvania Avenue NW.

The twin-turreted building most recently housed the Apex Liquor Store and has been a prime target for redevelopment for several years. The 123-year-old complex is known officially as the Central National Bank building and includes two adjacent buildings, one of which served as the studio for the renowned Civil War photographer.

Sears executives refused to comment on the purchase yesterday. But the Chicago-based retail giant has called a press conference for next Monday.

Officials of the Pennsylvania Avenue Development Corp. will be there, too.

Invitations distributed yesterday say Sears President Archie R. Boe will "unveil Sears' plans for joining in Pennsylvania Avenue restoration and establishing its world trade headquarters in Washington."

Washington real estate sources said renovation of the buildings will be complete sometime around the end of the year.

The Sears World Trade building is halfway between the Capitol and the White House with sweeping views of the presidential parade route from its tiny towers. The cost of purchasing and renovating the historic buildings has not been disclosed.

Washington developers have been working on the renovation project for several years, but the project has been delayed by high interest rates and the extraordinary cost of refurbishing.

The retailer's new trading company was set up last year not only to import products for the vast network of Sears department stores, but also to put together complex international deals.

The trade subsidiary recently found British retail outlets for U.S. power tools. It put together a barter deal between foreign firms willing to swap Dominican sugar for breeding swine. It is training the management of a chain of Chilean department stores.

Recruited by Sears to head the new international trading company are former SEC chairman Hills, who is chairman of Sears World Trade Inc., and Carlucci, a veteran of several Republican administrations who joined Sears' new subsidiary as president in December.

International trade is one of several new fields the retailer has entered in recent years.

In 1981, Sears bought the big Wall Street firm Dean Witter Reynolds Inc. and the real estate broker Coldwell Banker. It has long owned a big insurance business, Allstate Insurance Co.

The company's move into new areas was motivated in large part by what it sees as a slowing in the growth of retailing.

Last year Sears introduced new "financial" centers into eight of its stores, hoping that putting Dean Witter, Coldwell Banker and Allstate into the same location would lure a new breed of customer to a financial supermarket.