The Maryland state pension reform bill easily won preliminary approval in both the House and the Sentae today, prompting legislative leaders to predict the measure will face only minimal opposition this year -- a signal of how much the political climate here has changed in the past 12 months.

One year ago, in the preelection session, a similar bill revamping the pension system for teachers and state workers was killed after a bitter and protracted debate. That defeat was in large part the result of intense lobbying by members of the teacher and state employe unions, who constantly reminded delegates that their votes might be held against them in the November election.

This year, with the election out of the way, the new General Assembly leadership and the new governor, Harry R. Hughes, made the pension reform bill one of the top priorities of the session and set in motion a finely tuned and coordinated effort to steer the measure through the legislature.

The strategy was prepared in early January on the eve of the 1979 session when Hughes called House Speaker Benjamin Cardin and Senate President James Clark Jr, to his secondfloor State House office and worked out an agreement that no amendments would be added to the bill unless all three men consented.

This was the first contrast from last year's deliberations, when former Acting Gov. Blair Lee III and former Senate President Steny H. Hoyer, both then running for governor, constantly were feuding behind the scenes over how the pension measure should be handled.

In the month following that initial meeting, Hughes and the legislative leaders -- now including the chairmen of the House and Senate committees that would first consider the bill -- held two meetings with representatives of the teacher and state employe unions.

At the first meeting, the union leaders were asked to list their objections to the bill and what changes would make it acceptable to them. At the second meeting, they were asked to rate -- or, in bureaucratic jargon, "prioritize" -- their suggested changes.

"We established right awat that we couldn't satisfy all their (the unions') desires, but that we would work with them very closely," said Cardin this morning. "They offered two amendments that we could accept on merit, and that teally turned the trick politically."

The bill that both houses tentatively approved today would set up an entirely new companion pension system covering teachers and state employes hired after this year.This new system would differ from the existing system, which covers about 70,000 state employes and teachers, in two kdy respects:

It would reduce annual retirement payments by at least 20 percent for employes hired after Jan. 1, 1980. For an employe whose highest threeyear average salary was $15,000, for example, the yearly pension benefits would drop from $14,100 to $10,800 before cost-of-living increases.

It would limit cost-of-living increases for pensioners to 3 percent annually, unlike the present system, which requires cost-of-living increases equal to the annual jump in the consumer price index.

These changes in the pension system were based on a study completed two years ago that concluded that unless the pension ststem was severly modified the state was in danger of going bankrupt by the year 2020.

The new pension system would not affect current teachers and state employes unless they voluntarily decide to join it. As an incentive for them to do that, the new system,drops the existing requirement that employes contribute 5 percent of their salaries toward the pension fund.

One amendment that was added to the bill in committee last month and, as Cardin said, "turned the trick politically," provided a written guarantee that the existing system would not be altered in any way. This guarantee was eagerly sought by the employe groups, who feared that the new system would be imposed on them at a later date.

The other amendment accepted by the leadership and both houses today permitted employes to retire with full pension benefits after 30 years seryice. In its original form the legislation granted full benefits only to persons who had reached age 62.

"The amendments were very important, no doubt about it," said Thomas Gray of the Maryland State Teachers Association. Gray said his union still opposed many aspects of the pension bill, but he added: "Disappointment is a relative thing."

Del. Gerard Devlin (D-Prince George's) who opposed last year's bill, supported the bill with amendments this year as did almost all Prince George's delegates. Alst year, as the core of the opposition, this group developed a reputation as the most teacher-oriented delegation in the House.