DENVER, FEB. 24 -- The Oil, Chemical and Atomic Workers International Union (OCAW) has rejected a merger with the United Mine Workers, shattering the hopes of UMW President Richard Trumka for creation of a national energy union.

Such a merger also was seen by many in the labor movement as the mine workers' first step toward joining the AFL-CIO.

For Trumka, OCAW's rejection Tuesday was the first major defeat of what has been a meteoric six-year career as UMW leader.

"I am obviously quite disappointed," Trumka said, adding that he is convinced that OCAW leaders dealt with him in good faith and that he came out of the experience "wiser and more determined."

Trumka said he is not sure why the OCAW board turned down the merger agreement but indicated that the question of future union dues may have been an issue. He said the OCAW board wanted to change the merger agreement so that dues could not be increased until well into the 1990s.

An OCAW spokesman said today that a series of matters, nothing in particular, led to the rejection.

Negotiators for the two unions reached tentative agreement late last week. The UMW approved the merger at a special board meeting here Sunday, but the OCAW board, after two days of deliberations, turned down the proposal, 6 to 2.

Had the OCAW board approved the merger, a vote on it would have been taken at the union's convention this summer. An earlier UMW convention had given Trumka and the board merger authority.

After the OCAW rejection, Trumka met with his board Tuesday night, and members voted to rescind the merger agreement. "I consider it a closed deal . . . ," Trumka said today.

The 200,000-member combined union would have been called the United Mine, Energy and Chemical Workers of America and been headed by Trumka. OCAW President Joseph Mesbrener would have been president emeritus.

The proposed merger, according to UMW officials, was part of a Trumka vision of a national energy union that would mirror corporate ownership of the nation's energy resources. Most major coal companies, for example, are owned by the oil industry.

In addition to the OCAW, the mine workers have been looking at other unions as potential partners.

UMW officials will not name these other unions, but the International Chemical Workers Union is believed to be a potential candidate.

Merger of the UMW, OCAW and chemical workers, for example, would match the production of a company such as E.I. du Pont de Nemours & Co. which, in addition to being a major chemical manufacturer, owns Conoco Oil and Consolidation Coal.

"I'm going to come back to my next board meeting with a new game plan," Trumka said. That is expected to name potential merger partners. The UMW board is to reconvene at the end of March.

Trumka listed the coal, oil, gas, hydroelectric and atomic energy industries as potential areas to be brought under the umbrella of a single energy union.

In addition to possible future mergers, he said, the UMW would look outside the energy area for future organizing activities. He said the UMW board has "voted unanimously to pursue a policy of growth."

Although UMW officials said there is no bitterness toward the OCAW, some expressed anger and frustration. "We came out of the mines with a vision, and this is our first failure," one said. "We're used to winning."