Half a million people telephoned -- or attempted to call -- the government Friday to find out if it was true they really could get a silver dollar coin for only $65 paper dollars.

One hundred thousand letters with checks or money orders, arrived at the General Service Administration office in San Francisco yesterday morning. Each of them contains a bid for one or more of the 299,390 silver dollars Uncle Sam is selling for between $45 and $65.

Toll-free government telephone lines (with the 800 prefix) have been jammed off and on since GSA announced the sale of the Carson City silver dollars. Officials think the worst is yet to come in one of the strangest mail-order offers in history.

In one hour-long period, from 3 to 4 p.m. Friday, 25,000 people called or tried to call the toll-free number (800-336-4745) GSA advertised, in newspapers and on radio, for recorded information on the silver dollar sale. i

(Locally that number is 755-8660. Expect a busy signal).

With interest in precious metals at an all-time high, Americans with too littles money -- or too much sense -- to plunge into gold speculation are buying anything silver. The price yesterday had gone up to $39.15 an ounce. The silver dollars weigh 142.5 grains and are 90 percent silver.

Federal officials anticipate much more interest this time than they had in 1972 through 1974, when the government sold 2 million silver dollars for $55.3 million.

Because of the heavy demand this time, GSA brass in charge of silver think it may be late summer before some people whose bids are accepted will be receiving their coins. In addition to the value of the silver, and the collector's value of the 1878-through-1893 coins, lucky bidders will get another bit of Americana which is not causing chuckles at the White House: Each packet with a silver dollar also contains a message from the president, advising the lucky buyer that he or she is getting a bit of history. Unfortunately, for the politically-conscious the messages were written and signed by Richard M. Nixon.

Sidebar: There was some comic relief at a swamped GSA office this morning, where workers were digging out from under piles of mail, and telephone messages.

A caller got hold of a GSA official about her bid for a silver dollar. She said she had sent it to the Washington office along with her money order. But she thinks she forgot to sign the money order or to put her return address on the envelope. When it turns up, she asked, would somebody call her so she can get it back for signature. The man she talked with reportedly is in a mild state of shock.