Representatives of the Defense Department and the National Security Council have agreed to clarify language in a controversial security clearance form that bars federal workers from disclosing information that might be "classifiable" sometime in the future.

The agreement clears the way for Senate action on the names of nearly 9,000 military and civilian personnel, some of whom have been awaiting promotions since June. The promotion list was put on hold by critics of a security form, called SF 189. The form, which must be signed by civil servants in order to get or keep a security clearance, pledges them not to disclose data that might someday be considered classified.

Sen. Charles E. Grassley (R-Iowa) put the hold on the nominations. But an aide said NSC and Defense officials had met with Grassley and an aide to Sen. John W. Warner (R-Va.) and had agreed to provide a "more restrictive definition of the term 'classifiable' " in the form. Grassley in turn agreed to remove the hold on the promotion list. Warner is interested in the issue because of the large number of federal and high-ranking military personnel in his state.

The promotion list, which boosts not only the rank, includes the names of military personnel in line for promotions from colonel to general and admiral, as well as civilian political appointments that must be okayed by the Senate. Civilians on the list include top appointees at the departments of justice and labor, as well as Commerce Secretary-designate C. William Verity Jr.

Grassley and others used the promotion list as a pawn to bring Reagan administration officials to the bargaining table on the subject of the form's wording and intent. Although administration officials played down the impact of the form, some Senate and House members say they have been contacted by civil servants who said they were afraid to sign the form, but were being pressured to do it or lose their security clearances and perhaps their jobs as well.

Grassley said the form had a potentially chilling effect on federal workers, and could make employes afraid to blow the whistle on fraud and waste in government.

A similar security clearance form required of private contractors working for the government does not refer to material that might be "classifiable" in future.

Most of the government workers required to sign the form work for the Defense Department or are in agencies handling classified material. Because of a pending lawsuit challenging the "vagueness" of the language in the form, the government has agreed not to require employes to sign it until there is a decision from the U.S. District Court for the District of Columbia.

A spokesman for the National Federation of Federal Employees union, which brought the lawsuit, said it was "too early to comment" on the Defense-NSC agreement until the union sees what language will be used to define the term "classifiable."

Retirement Income

Computer projections show that nearly half of all government workers would get bigger pensions under the new Federal Employees Retirement System. Workers hired before 1984 have until Dec. 31 to decide whether to switch to FERS, or stay with the current retirement program.

At 1 p.m. tomorrow on WNTR radio (1050 AM), representatives of SORT Inc. will do free computer benefit projections for listeners.