A new threat to the back-to-work movement in the Appalachian coal-fields emerged yesterday as trustees of the miners' strike-depleted benefit funds warned that pensions as well as health payments, may have to be cut next month.

Just as a 10-week wildcat strike over earlier health-benefit cuts appeared to be ending, trustees of the United Mine Workers Health and Retirement Funds announced that a new round of cutbacks "may be necessary."

Income to the UMW funds - which provide health benefits to 811,000 and pensions to 81,500 - comes from royalties from coal production. Hence, with up to 85,000 of the union's 175,000 working miners out of work for varying periods of time during the strike, income to the funds has been reduced by about one-third.

Although nearly all the mines were reported returning to normal operations this week, the October benefits will be in jeopardy because they are based on production from August, when the strike level was high.

The trustees had to borrwo $3.5 million to pay September pensions and, after paying off the loan, will have only $11.5 million to pay about $19.5 million in October pensions - leaving a shortage of $8 million, the trustees said yesterday.

Thus, they said, it "may be necessary to reduce or delay" payment of October pensions.

Barbara Moldauer, an official for the funds, said the only apparent alternative to cut or delay in pension checks is a rescheduling of income payments from the coal operators. A spokesman for the Bituminous Coal Operators Association, the industry's bargaining group, said the BCOA will consider "all options," including another loan. But Moldauer said "it doesn't look like anyone will lend us the money at this point."

The trustees said the health funds are in a similar situation and may also have to be cut again. Cuts that were ordered in July - partly as a results of a previous round of wildcat strikes - forced miners to pay up $500 a year for health services that were previously free.

It was this action that promted the latest 10 weeks of wildcate strikes, which were estimated to be costing the funds about $1 million a day at their peak.

Pension benefits were not affected by the July cutback.

Both union and industry officials have privately expressed fears that a new round of cutbacks might trigger more wildcate strikes. The miners agreed to call off their walkout for 60 days late last month to permit time for a negotiated settlement of the benefits problem. The 60 days run out in late October.

UMW President Arnold Miller and BCOA President Joseph P. Brennan are scheduled to meet Friday to discuss the problem, although Brennan has said he will not agree to a royalty reallocation that Miller has demanded.

Meanwhile, a group of dissident miners in Marmet, W. Va., began circulating petitions to recall Miller on charges that he concealed knowledge of the July cutbacks before his re-election as union president - a charge Miller has denied.