It seemed like a simple enough request when Republican Sen. James A. McClure asked his colleagues last week to grant speedy approval to a bill that would create a Statue of Liberty commemorative coin.

But the gambit failed just before the Easter recess when other senators discovered that McClure was planning a silver-plated version of the bill. The senator from Idaho, where nearly half the nation's silver is mined, was ready to tack on his perennial amendment to authorize the Treasury to mint millions of one-ounce silver coins.

McClure has been pushing a similar measure for the last three years and never gotten it out of the Senate Banking Committee. This time he tried to short-circuit normal procedures and move the popular Statue of Liberty bill right to the Senate floor, where he believed he had enough Republican support to weld it to his silver amendment.

But Sen. William Proxmire (D-Wis.) quietly blocked the maneuver, saying no one had seen a copy of McClure's amendment and the Banking Committee never held hearings on it.

McClure, chairman of the Senate Energy and Natural Resources Committee, was following a tradition that dates to the 1880s, when western lawmakers regularly fought for silver coinage bills in Congress as part of a "free silver" movement.

Bill Livingstone, a spokesman for McClure, said the senator believes his amendment is the best method for disposing of some of the 137 million troy ounces of surplus silver in the nation's strategic defense stockpile. He said this is preferable to having the silver "dumped on the market" in a public sale, which silver producers fear would depress market prices.

Livingstone acknowledged that other senators haven't seen McClure's amendment, but said it is similar to a bill that McClure sponsored last year, which would authorize the Treasury to mint 90 million silver coins for sale to the public at about $15 apiece.

A number of silver mines in Idaho have been shut as the industry has struggled through several years of low prices. "That's part of the senator's interest," Livingstone said.

The bill to sell 35 million Statue of Liberty coins to help restore the decaying landmark generated no controversy when it passed the House in February. It thus loomed as the perfect Senate vehicle for a quick amendment before the recess.

McClure needed unanimous consent from all Banking Committee members to bypass normal rules and move the bill to the floor. He had made known that he planned to tack on the silver amendment, and the panel's Republicans all consented to the plan.

Proxmire, the panel's ranking Democrat, said McClure assured him the silver amendment would not be controversial. He said McClure told him "that nobody would object to it and it would breeze right through."

But Proxmire said that after checking with his staff, he found that the Treasury Department had objected to the measure and that he could not obtain a copy. "We ought to at least know what we're doing," said Proxmire, who refused to give the required unanimous consent.

Proxmire also learned that three other senators planned amendments to direct the Treasury to mint gold coins to compete with South African Krugerrands. This virtually ensured that the bill would be mired in debate and could not be approved before the Senate adjourned for Easter.

The issue first heated up in late 1981, when the Reagan administration sold 2 million troy ounces of excess silver from U.S. stockpiles in West Point and San Francisco. Silver dealers blamed the announcement for a drop in prices from $10.96 to $9.72 an ounce, and the government scrapped plans for a much larger sale.

Some experts question whether the auction had anything to do with the slide in the silver price, which later bottomed out at $4.88 an ounce and since has risen to $6.70. But McClure quickly pushed through an amendment to the 1982 defense appropriations bill that has halted any further silver sale until the administration certifies that it will not disrupt the market. The administration still is studying the issue.

The Silver Users Association, representing jewelry, photographic, silverware and other companies, contends that a major silver auction would boost federal revenues without affecting market prices. Walter Frankland, the group's vice president, complained that McClure's coin proposal "denies our members access to the silver. They would not want to buy coins."

McClure has cited industry studies that say there is a big market for silver bullion coins. But a spokesman for U.S. Treasurer Katherine D. Ortega said her office has "reservations and concerns" about whether the silver coins would "saturate the market" and whether the Treasury can handle two coin programs at once.

Livingstone said that Rep. Frank Annunzio (D-Ill.), sponsor of the Statue of Liberty bill, agreed to support McClure's amendment, but an aide to Annunzio said he knew nothing about it.

The Statue of Liberty bill also proved irresistible to Sens. Alan Cranston (D-Calif.), Robert J. Dole (R-Kan.) and J. James Exon (D-Neb.), who indicated they would add gold coinage amendments to protest South Africa's apartheid policy.