Martin Marietta Corp. is trying to develop a set of sophisticated weapons that neither sleet nor rain nor dark of night can keep from their appointed targets.

Martin Marietta last week received a $14.5 million contract from the Defense Advanced Research Project Agency (DARPA) to examine the next generation of "smart" weapons, which have more sensitive infrared sensors and better signal-processing capability than current weaponry.

Infrared sensors detect slight differences in heat, which can be translated into pictures of a scene. Infrared works well in daylight and darkness, but during periods of heavy precipitation it can be inaccurate; in those circumstances, "millimeter-wave" radar can be used is used to generate an image.

The Defense Department now uses these technologies in the F15 and F16 fighters and in the Apache helicopter.

DARPA, a Defense Department agency that conducts research for the armed forces, is stuyding the use of "smart" technology in unmanned aircraft.

The key to the new weaponry is "geometric arithmethic parallel processing," or GAPP, said Phil Giaramita, director of public relations for Martin Marietta's electronics and missiles group.

GAPP equipment can process many pieces of information at the same time and use it to create a faster, clearer image. In unmanned aircraft, smart weapons could be used to locate mobile targets that are hidden from sight.

Martin Marietta's electronics and missiles group will develop the advanced avionics and software necessary for the system.

"The software tells what kinds of characteristics to look for. For example, when heat is concentrated on the road in a specific way, the system realizes the object is a tank," Giaramita said.

"This technology helps even up the score on conventional forces in Europe," he added. "The North Atlantic Treaty Organization is at a substantial disadvantage in the number of troops, tanks and ground forces, compared to the U.S.S.R. and the Warsaw Pact countries. We are trying to offset that disadvantage by developing technology that is more accurate and needs fewer men than the traditional weapons.

"Actually, the defense budget would have to be double what it is now if we tried to match the Soviet Union in conventional forces. With technology, we stay ahead of the enemy threat," Giaramita said.

Giaramita expects the smart-weapons technology to have spinoffs in other systems.

"This is a very broad contract to study the feasibility of using smart-weapons technology in a number of different ways. But there is no commitment on the government's part to start producing unmanned aircraft with smart weapons technology," he said.

Theoretically, the technology could have commercial uses in rescue helicopters and other vehicles that need to distinguish objects from afar. "But we would have to produce it cheaply," said Giaramita.

Editorial Experts Inc. in Alexandria is cleaning up the U.S. Army's English for $1.1 million.

The Defense Supply Service-Washington has awarded Editorial Experts a three-year contract to edit the Army's written regulations.

The project's goal is to cut unnecessary detail and duplication and to reduce the number of regulations by at least one third.

This is the largest single contract awarded to the publications services firm since its founding in 1972.

MCI Communications Corp. is now the sole vendor for direct dial long-distance calls from the Pentagon and other Defense Department. The five-year contract has a potential value $30 million.

Under the contract, MCI will consolidate existing WATS and foreign exchange services that had been provided jointly by MCI and American Telephone & Telegraph since 1981.

Contract negotiations with the Pentagon were coordinated through MCI's Government Systems Group, which specializes in communications services for the federal government.

Second National Federal Savings Bank is entering the Baltimore market by opening a branch in the city this month and merging with Brehm Federal Savings Bank, a mutual institution with three offices in the Baltimore area.

Second National is a $820 millioncompany with 27 offices in Maryland and Delaware.

It expects to complete the merger with Brehm Federal, worth about $70 million, by January.

Brehm Federal will change its name to Second National after the merger, according to William T. Russell, senior vice president and treasurer of Second National.

The merger is subject to approval by the Federal Home Loan Bank Board.

Cadmus Communications Corp. in Richmond is purchasing two graphic communications firms -- Garamond/Pridemark Press in Baltimore and Dataset Communications Inc. in New York.

Garamond/Pridemark specializes in high-quality, full-color offset lithography. Dataset is a preset company that specializes in books and periodicals. Both firms are privately held.

"We have a strategy of expanding operations into contiguous markets," said Wallace Stettinius, chief executive of Cadmus. "Garamond/Pridemark will complement our sales and service in the Washington market, and Dataset will provide our William Byrd Press subsidiary with a typesetting facility in the largest periodical market in the world."

Cadmus is a graphics and printing company that reported sales of $115 million last year.

United Savings Bank, a $430 million savings and loan association in Virginia, is buying Severn Savings Bank FSB, a $50 million S&L in Maryland.

Under the agreement, Severn shareholders will receive United common stock and cash valued at $14.50 for each of the 500,000 shares of Severn common stock and 190,000 shares of Severn preferred stock outstanding.

"United has no intention of altering Severn's approach to business," said Howard D. Orebaugh, president of United. The existing management of Severn will be retained.

Alan J. Hyatt, president of Severn, will be appointed to United's board, and Melvin E. Meekins Jr., executive vice president of Severn, will be appointed regional vice president for United.

The Sheppard and Enoch Pratt Health System in Baltimore is expanding into the Washington area through a joint venture, called Newco, with Medlantic Healthcare Group.

Newco will provide Sheppard Pratt's mental health services in Medlantic's health care facilities in the District, Maryland and Northern Virginia.

Specifically, Newco will manage mental health units for both companies and develop mental health education and employe assistance programs. The new company will also establish cooperative psychiatric residency programs between Sheppard Pratt and Medlantic.

Dr. Robert Gibson, president and chief executive of Sheppard Pratt, will become president of the new corporation.

Newco's board will include three trustees from Sheppard Pratt and three from Medlantic.

Medlantic employs more than 7,000 people at Capitol Hill Hospital, Columbia Hospital for Women Medical Center, National Rehabilitation Hospital, the Washington Hospital Center and other patient care centers. Sheppard Pratt runs a 332-bed hospital with a staff of 1,100. Hay Systems Inc., part of Hay Group in the District, is studying the general and flag officer positions within the Joint Chiefs of Staff under a $490,000 contract.

The survey is the first step in meeting the provisions of the Goldwater/Nichols Department of Defense Reorganization Act of 1987. The act requires that general and flag officer jobs be graded, and calls for the consolidation of military department responsibilities and a decrease in headquarters and defense agency staffs of about 16,500 people.

The purpose of the Hay Systems contract is to evaluate the responsibilities of different officer positions. It will conduct interviews and hand out questionnaires to about 285 staff members. Hay is not examining the officers themselves, it is focusing on their duties.

Resource Consultants Inc. has been awarded a $4.8 million contract by the Space and Naval Warfare Systems Command to produce technical publications.

Under the three-year contract, RCI will develop technical manual programs for electronic equipment.

RCI, based in Vienna, provides engineering and professional services to the government.