Citing soaring costs and declining income, the Montgomery County Council yesterday took away from 6,000 employes a guaranteed cost-of-living increase that employes accepted six months ago instead of an automatic annual raise.

Voting 3 to 2, before a group of stunned employes, the council said the policy reversal was necessary to avoid putting a fiscal straitjacket on the newly elected council and to leave enough flexibility in the budget to permit the county to pay for all its vital programs and live within a voter-imposed budget ceiling.

"This is a dirty trick," said Jack Jardelera, head of the Montgomery County Government Employes Organization, one of several employes groups. "This was a deal that the administration had made with the employes as part of a total [personnel] package."

Council member William Colman, who voted against the policy reversal, agreed, calling the cost-if-living guarantee a "quid pro quo" in a com, promise with employes over a sweeping new pay plan adopted by the council last spring.

"Council members will recall this was part of a significant reform package, a step in the right direction for our employes," said Council President Elizabeth Scull, who voted with Colman. "And so it is with a mixture of disbelief and heartbreak I watch the council sabotage its own reform."

"You can't trust the people you place in office," charged Pvt. Leonard SImpson, head of the Fraternal Order of Police, which represents two-thirds of the county's 740-member police force. "They said one thing and then after they wer reelected, they turned around and did another."

The cost-of-living change of heart came yesterday as the council put the finishing touches on two bills that are part of a comprehensive merit system "reform" in the county.

One law, which was passed unanimously, delineates personnel policies and procedures for resolving employe grievances. It also includes a "whistle-blower" provision that protects merit system employes from retaliatory or coersive action or disclosing information about illegal or improper activities within the government.

The pay plan bill, however, was more controversial.

When the pay plan revisions were first decided on in May, they included a section under which employees' annual logevity increases were decreased from 5 percent to 2 percent and pay increases were tied more closely to job performance. In return, however, employes would have received a guaranteed yearly cost-of-living increment of not less than 75 percent of the rise in the inflation index.

The decision to review the cost of living provision occured yesterday when the council, rushing to complete its term by the end of the month, was creating the policy of last May into a binding law.

Moving to delete the cost-of-living guarantee. Councilman John Menke proposed instead that the allowance be paid employes only if there is extra money in the budget.

"We can talk about what is fair, right and just, but the money is not there," Menke said. "This is a majo-sten. writing into law, what must be in the county executive's budget . . . It's bad legislation that does not protect the public interest."

County officials have estimated the new pay plan revisions will save about $7 million over the next firve years, while elimination of the cost-of-living guarantee would reduce spending another $25 million next year.

The cost-of-living adjustment alone would give the average em love, who make $18,000 with fringe benefits, about $1,200 in additional income.

The county's fiscal planning is newly complicated by passage of Question D, a charcter amendment to limit annual budget increases to the cost of living unless five of the seven members vote to override the requirement.

Mention of that new charter provision led council member Esther Gelman to change her original vote against Menke's proposal and thus assure its passage.

"I suddenly saw it in its full complexity, Gelman said. "When we were first talking about this, Question D hadn't been approved or passed . . . The requirement of an extraordinary majority always bothers me."