United Mine Workers President Sam Church Jr. easily won the right today to handpick his vice president.

The voice vote giving Church the one-time power was seen as a major rank-and-file endorsement of his leadership.

The vote came at the union's 48th constitutional convention after less than an hour of debate, in which Church took part.

Church 43, who succeeded the ailing Arnold Miller on Nov. 16, sought the appointive power on the ground that a vice presidential election now would place undue policical and financial pressure on the frequently belligerent and currently broke union.

Today's vote was on a one-time waiver of the UMW constitutional provision on the election of union vice presidents.

Some of the estimated 1,200 delegates attending the 10-day union meeting strongly opposed the waiver.

"The vice president should and could be a catalyst to the president. He should not be a 'yes man,'" said delegate James Tomb of Ebensburg, Pa.

"Whatever the cost of an election, I don't think it's too much of a price to pay to prevent ourselves from being sold back into something we fought to getout of."

His reference was to the hardfought battle waged by the UMW rank and file in the late 1960s and early 1970s to rid itself of autocratic leadership. The dispute led to the December 1969 murders of movement leader Joseph A. (Jock) Yablonski and two family members. Former UMW president W.A. (Tony) Boyle was convicted of murder in the case, and was ousted from his union post in 1972 by "union reformer" Arnold Miller.

But Miller's reign also was marked by dissension and a continued decline in union finances and prestige.

The majority of the 1,200 delegates here said today they were tired of the status quo and that they were willing, as one delegate put it, "to temper democracy a little" to make some progress.

Union officials said the election of a vice president to complete the term expiring in December 1982 would have cost the union at least $750,000. The vacancy was created by Church's elevation to the presidency.

In today's debate, Church said he "ccould live with it either way" -- an elected or an appointed vice president. But observers thought Church was covering himself in the unlikely event that the convention voted down the proposed constitutional waiver.

Church ended his remarks by reminding the delegates that UMW elections are often divisive. "You know what happens . . . and you know how the press feeds upon it," he said.

The voice vote took less than a minute. No one asked for a headcount.

Church said Monday that he had "several good people in mind" as vice presidential prospects. He did not name them, nor did he say when he would announce his selection.

The meeting here is costing $2 million, which will virtually deplete the union's liquid assets.

"We will be down to zero" wen the convention ends Dec. 20, said Willard A. Esselstyn, the union's secretary-treasrer. For this and other reasons, the union desperately needs proposed increases in dues and fees, he told delegates today.

Voting on the proposed increaseses scheduled for Wednesday.