Striking United Mine Workers members prepared to vote today on their latest contract offer as union officials scrambled to refute a wave of coalfield rumors that could undercut ratification prospects.

After 108 days of striking, the 160,000 UMW miners are reportedly more inclined to return to work than they were three weeks ago when they voted by more than 2 to 1 reject an earlier offer.

But reports from the coalfields indicate the vote is too close to call in advance. Voting is expected to be concluded late today, and the result may be known as early as tonight.

Complicating the outlook were two recent developments: circulation of leaftlets charging that the contract envisions elimination of many existing health benefits and UMW leaders' inability to disburse speedily more than $2.4 million in relief money donated by other unions.

Reacting to the benefit cutback charges, UMW President Arnold Miller sent telegrams to all union district leaders denying any change in health benefits. The text, which was released to the press, did not mention the fact that miners, for the first time, would have to pay up to $200 a year in medical costs.

In response to other miners' claims that relief funds were being withheld to influence today's vote, UMW Secretary-Treasurer Willard A. Esselstyn called a press conference to say that the money is being distributed as rapidly as possible.

Esselstyn's statement did not say how much had been given out thus far and he refused to anser questions on the subject.

According to the statement, $2.4 million in cash and checks has been received so far. Pledges totaling $2 million have also have been received from the United Steelworkers and the Communications Workers.

Esselstyn denied "categorically" that the relief money was being withheld to affect the vote and indicated delays were attributable to legal requirements for proper accounting of the funds."They're mired down in their own red tape," said one source familiar with the disbursement problem.

The United Auto Workers, which donated $2 million of the $2.4 million cash fund, was quietly pressing UMW officials to "cut the red tape as quickly as possible," and auto workers official said.

A "yes" vote on the contract could have most of the stuck coal miners, which produce about half the nation's coal supplies, back in operation next week. A "no" vote could lead to another round of negotiations or a breakup of industrywide bargaining.

Labor Secretary Ray Marshall met late yesterday at the White House with other administration coal strike strategists on what to do if the contract were rejected. A source indicated the administration was "moderately optimistic" that the contract would be approved but wanted to be prepared it if wasn't.

Sources indicated after the meeting that the government was undecided on what to do it the contract goes down again, including whether to push for a full Taft-Hartley injunction against the strike. A federal judge refused to extend a temporary back-to-work order last week, complaining the government was not enforcing it and had not shown that a national emergency exists.

The Justice Department was reportedly pushing the Taft-Hartley course, but a decision was put off until after the vote. Asked earlier in the day about the government's plans, White House spokesman Jody Powell referred to statistics showing that, even with the strike, utilities are getting 77 percent of their normal coal supplies nationally and 72 percent in the hardhit East-Central region. Other government sources suggested that this minimize the need for immediate government intervention.

The contract, the third to be negotiated since the strike began Dec. 6, includes some major industry concessions, including abandonment of wildcat strike penalties and a reduction of proposed annual health care deductibles from a maximum of $700 to $200.

But many miners were still complaining about the deductibles, company takeover of the health care system that was previously administered by independent trustees, failure to equalize pensions and new production incentives, among other things.

Of less concern were wages, which would rise from an average of $7.80 an hour to $10.20 over three years. The total cost of the package is about 39 percent, up about 2 percent from the previous offer. It is the largest gain for a major union since the UMW got an increase of more than 50 percent in 1974.

Reasons most frequently cited for optimism over ratification include the industry concessions, a feeling (not universal but widespread) that the union has gotten about all it's going to get, fear of a breakup of industrywide bargaining and its impact on the already fractured UMW, and steadily increasing financial pressures on the strikers and their families.

Also, the union abandoned the controversial Madison Avenue-style sales pitch it used for the vote three weeks ago and relied almost exclusively on local and district union officials to sell the contract. Some were doing so with more vigor than others.