Baltimore Superintendent Walter G. Amprey has sent a form letter to all 10,000 city school system employees warning that a "considerable number" of them will be reassigned or laid off by June 30.

In the letter, dated Thursday, Dr. Amprey called the impending reassignments and layoffs a result of last-minute budget adjustments and the system's effort to move more money, staff and authority from headquarters to individual schools.

"I must inform you that a considerable number of employees . . . will be subject to reassignment and/or released, effective with the close of business on June 30, 1994," the letter said.

It said the changes would affect all union bargaining units -- groups that represent teachers, principals, paraprofessionals, secretaries and maintenance workers, among others.

The one-page, single-spaced letter -- the first such warning to all school system employees in at least a decade -- triggered waves of shock, anger and anxiety when it began arriving in employees' home mailboxes Saturday. It drew immediate criticism from the 8,500-member Baltimore Teachers Union as a threat aimed at influencing the outcome of current contract negotiations.

The notice marked the first time Dr. Amprey has publicly raised the possibility of systemwide layoffs. A school system spokesman, Nat Harrington, said he could provide little information yesterday about the possible scope of the coming changes or which employees might be targeted.

Dr. Amprey, who left for Israel the day he sent the letter, could not be reached for comment. Mr. Harrington said Dr. Amprey is not vacationing, but he could not say why the superintendent was in Israel, with whom or who financed the trip.

Mr. Harrington said he doubted the superintendent plans "whole sale layoffs of any teachers." But, even though Mayor Kurt L. Schmoke's budget includes money for 81 more teachers, Mr. Harrington said: "I can't say with certainty that we're not talking teachers. Everything's up for grabs, but the problem is, at this point, we don't know who or how many will be affected."

As the district moves toward school-based management, Mr. Harrington said, some principals may decide to eliminate teachers who specialize in certain areas, such as teaching "gifted-and-talented" students. That could result in reassignments or layoffs, he said.

Budget adjustments -- which will depend in part on how big a raise results from current contract negotiations -- also will have a bearing on how many employees are reassigned or laid off, Mr. Harrington said.

Dr. Amprey's letter said that "in the next few days," Deputy Superintendent Patsy B. Blackshear would discuss % reassignments with affected employees or, in cases of layoffs, severance pay and benefits.

"I understand and sympathize with the concern this letter undoubtedly causes," Dr. Amprey's letter stated, adding that the decision was "very painful and regrettable."

Linda Prudente, a spokeswoman for the teachers' union, said city negotiators had never raised the prospect of layoffs or reassignments of anyone outside school system headquarters during five months of bitter talks, which have stalled.

"The timing's definitely suspect," she said. "Clearly, if they were in such dire straits financially, they should have told our negotiating team. This seems to be posturing at this late date to get the contract signed and give employees as little as possible."

One City Council member agreed. "I don't see how teachers could view this as anything but a threat," said John L. Cain, D-1st. "But I don't think it will get them to back down."

Last month, Dr. Amprey announced a "major, major shake-up" that he said could result in hundreds of headquarters employees being demoted or moved to other jobs as the school system shifts more authority, money and staff members from headquarters to individual schools.

He told his 177 principals that he's giving them more autonomy to run their schools by letting them control $32 million now controlled by school headquarters. Decentralization, which began with 24 experimental "enterprise schools" this year, will give individual schools much more say in spending for libraries, janitorial staff, teacher training, programs and other services.

Overall, the school system's operating budget for 1994-1995 will rise about 2.7 percent, to about $634 million, if the City Council approves the mayor's proposed spending plan.

Mr. Schmoke's spokesman, Clinton R. Coleman, said the mayor had approved the letter, after ordering changes to an earlier version because of concerns of "wording in such a way that it seemed to be a layoff notice."

Dr. Amprey had told the mayor that he planned "significant reductions" in central office staff, Mr. Coleman said. But because individual schools will have much more say over staffing, programs and budgets, Mr. Coleman said, it's hard to predict the number of teacher layoffs, if any.

The teachers' union views the superintendent's notice, in part, as retribution for the union's high-profile fight against school privatization.

"He is very angry over the fact that unions have not supported privatization," Ms. Prudente said. "He's said all over the country that teachers' unions are leading the fight against privatization for self-serving reasons. If he wants a fight on his hands, well, he's got it."

The union and a growing number of other critics, including a half-dozen City Council members, have called for a halt to expanding Education Alternatives Inc.'s role in city schools before a formal evaluation of its work.

The for-profit Minnesota-based company, the harshest critics complain, gets preferential treatment -- and more money -- at the expense of other schools, though it has failed to demonstrate improvements beyond fresh paint, cleaner schools and computers.

EAI-run schools receive more money per-pupil than most schools in the city, and the city is spending $8.5 million more this school year for the dozen schools EAI runs than would be spent if the company were not running the schools, budget documents show.

As Dr. Amprey moves toward expanding EAI's role, organized labor made clear last week that privatization will be a major issue in determining whom the unions back in city elections.

The day before Dr. Amprey signed the letter, six city unions lined up behind Councilman Lawrence A. Bell, an outspoken opponent of expanding privatization, in his bid to replace indicted Comptroller Jacqueline F. McLean. Mr. Bell has the backing of Mr. Schmoke's challenger in the Democratic primary, Mary Pat Clarke, a vocal opponent of school privatization.