In honor of the second annual observance of National Stamp Collecting Month this October, the U.S. Postal Service will issue a souvenir card featuring a die-stamped replica of perhaps this ccountry's best known error stamp -- the 24-cent air mail invert. The stamp reproduction comes close to matching the size and colors of the original but is much less expensive. The 1982 stamp collecting month card will be available over the counter at the nation's more than 300 local philatelic centers and by mail order from USP's Philatelic Sales Division for $2 in mint condition.

A canceled version, with a 35-cent Glen Curtis stamp affixed, is also available from the sales division in Washington for $2.35 each.

Collectors interested in obtaining either type of card by mail should forward orders to: Philatelic Sales Division, Washington, D.C. 20265-9990. Requests should specify whether the canceled or uncanceled card is desired.

Compared to one of the 24-cent inverts, this year's hobby card is a real steal. The current catalogue value of one of the 1918 inverts is about $150,000.

The 24-cent value was issued that year to meet the rate of postage and special delivery handling on mail carried on the first experimental air-mail route inaugurated between Washington, Philadelphia and New York, a distance of about 200 miles. This service was established May 15.

The day before the service was begun, William T. Robey, a District stockbroker's clerk, went to a local post office to buy a pane of the bi-colored air mail stamps for use on letters to be carried on the inaugural flight from Washington. That morning the branch post office had received a supply of the new stamp, but none of those on hand when Robey arrived was very well centered. Robey was told that if he'd come back that afternoon, perhaps a new supply would be available.

When he returned, he forked over three $10 bills and was given his $6 change and a full pane of 100 stamps. This time the faults that Robey saw with the stamps were definitely to his liking. He could hardly believe his eyes. What he had bought, he said later, made his heart stand still. The Curtiss Jenny vignettes had been printed upside-down.

In his excitement, Robey showed his find to the post office clerk who had sold him the stamps. The clerk quickly closed his sales window and grabbed for a telephone.

Smelling something was afoot, Robey, his possession safely tucked away, beat a hasty retreat.

Robey checked out other local post offices but failed to turn up any additional errors.

When he returned to work, he was greeted by a pair of postal inspectors who indicated they'd be more than happy to exchange his "mistakes" for "good" stamps. Unmoved, Robey refused to show them his discovery.

Robey's find soon became the talk of the town. Ultimately, the hounding got to be too much for him, and he sold the pane to Eugene Klein, founder and first president of the American Philatelic Congress, for $15,000.

Klein in turn sold the pane of stamps to Col. Edward H. R. Green for $20,000. Green initially broke the pane up into singles and blocks.

Over the years these have changed hands many times, and each time the price rises. Today, only 91 of the stamps can be accounted for.

The error was produced as a result of sloppy printing. For this two-color issue, the red frames and black vignettes were applied at different times. This required the sheet of stamp paper from which the error pane had come to go through the press twice, once to print the frames and again for the central designs. In this case, the printer placed the sheet upside-down on the second printing plate the second time around.

Only the one pane found by Robey escaped detection and was sold.

Because of the appeal of this postal issue, this isn't the first time the Postal Service has chosen to use the 24-cent air mail invert on a souvenir card. A replica of the popular error also appeared on the USPS's APEX '73 show tribute, released in honor of the International Airmail Exhibition held in Manchester, England, July 4-7, 1973.

This year's stamp collecting month card was designed by Jack Ruther of the Bureau of Engraving and Printing. The card, produced as Bureau Order No. 372-82, was ordered by the Postal Service on March 8.

The model for the card was forwarded Aug. 13 to the USPS and was approved the same day by Dick Williams, manager of the USPS's Stamp Management Branch.

Besides the die-stamped reproduction, this card bears a dedicatory message that points out, in part, "Stamp collecting engages the mind. The study of stamps, their thoughtful acquisition and display, the sharing of information about them and organizing, attending and participating in stamp exhibitions stimulates a better understanding of ourselves and the world around us. Because people of every age can find pleasure in these activities, stamp collecting is indeed 'the hobby of a lifetime.'"

The card's message, printed in black by offset, appears above a facsimile signature of Postmaster General William F. Bolger.

Flanking Bolger's signature to the left on this 6-by-8-inch card is the Postal Service logo.

Collectors interested in making a collection of stamp collecting month souvenir cards will have until Sept. 30 to order last year's hobby month tribute from the USPS's Philatelic Sales Division. At that time, the 1981 souvenir card, which is available for $2 canceled, will be withdrawn from sale. Orders should be addressed to: September Withdrawals, Philatelic Sales Division, Washington, D.C. 20265-9997. COINS

Idaho's congressional delegation has introduced legislation that would ressurrect the Morgan Silver dollar and enable the U.S. Mint to produce a new one-ounce silver bullion piece.

The measure calls for the use of up to 105 million troy ounces of silver from the national stockpile to be used to produce the two items in quantities that reflect public interest.

The bulk of the silver would be earmarked for the new bullion piece, 90 million troy ounces worth.

The bullion coin, labeled at this point the "SilVer Liberty," would contain .999 fine silVer and measure 1.6 inches in diameter.

The new Morgan dollar would match the size and composition of the earlier version, last minted in 1921.

Whether congressional leaders will have time to take up the legislation this session will depend upon how fast the Senate bill (S. 2598), sponsored by Idaho Republican Sens. James A. McClure and Steven D. Symms, and a companion House resolution (H.R. 6649), introduced by Idaho Republican Reps. George V. Hansen and Larry E. Craig, can be readied for a vote.

A spokesman for the Senate committee handling the Senate bill said no hearings have been scheduled.

Failure to take up the bill this session will mean the measure will have to be reintroduced during the next legislative term.

The House bill isn't moving any faster than the Senate bill. The measure is awaiting action by two House committees, and no hearings have been announced.

One reason for the slowness may be due to congressional concern over the possible affect passage would have on sales of the recently authorized precious metal commemorative Olympic coins to be offered by the U.S. Mint.

Besides helping the mining industry, a significant factor in Idaho's economy, the sale of the silver pieces would provide funds to buy more strategic material for the national stockpile, an aide to Craig said.