Pentagon officials have informally promised Sen. Charles Mathias (R-Md.) that they will not move any employees or units of the Defense Mapping Agency from Maryland.

Several weeks ago DMA announced that it was considering three options for its two commands in Brookmont and Suitland. One would be to consolidate top management at one of the two sites. Another proposal would be to shift either the 2,200 topographic command employees to Suitland, or move the 700 civilians of the hydrographic office to Brookmont. The third option was to relocate both the Brookmont and Suitland units to still another site. On April 1, this column said that either Pennysylvania or Illinois were possibilities.

Mathias and other areas legislators reacted quickly to the third option. The last time Defense studied the possibility of relocating a Maryland-based operation, more than 1,200 Suitland-based jobs of the Naval Oceanographic Office wound up in Mississippi.

Defense officials have advised Mathias that the out-of-state option no longer is a serious consideration. Knowing how these things work, Mathias is trying to get that pledge in writing - or better chiseled into granite.

Meanwhile, the Pennsylvania congressional delegation has high on its shopping list a request for a government installation to replace jobs at the Frankford Arsenal in Philadelphia. Despite a campaign pledge by Vice President Walter Mondale that Frankford would be kept open, it has been phased out. The White House is eager to appease angry Philadelphians and Defense officials are looking for a Washington-based unit with lots of civilian jobs that would fill the bill.