Congress has not yet received official notice of President Reagan's proposed budget cuts, but the cuts are already the subject of a lively debate.

So there may also be interest in Bernd Fossum's "Government Cash Request Form," which was sent to him in an envelope that urged, "Open and use at once.

When Bernd opened the envelope, he found advertising matter headed by type 50 percent larger than this newspaper normally uses for headlines at the top of page 1. The main heading said, "The Amazing Lost Money Secret of the U.S. Government." Smaller headlines said, "Does Uncle Sam Owe You Money You Don't Even Know About?" and, "Here Are 171 Surprise Ways To Get Money From Washington."

The text below said, "There is a very good chance you have some money coming from the U.S. Government. There is an even better chance you don't know why the government owes you this money or exactly how much you will get.

"The amount may surprise you. It could easily be a lot more than you would ever imagine. There is an honest chance you may have enough coming to retire on for the rest of your life."

The amount being given away is "astronomical," the text said, and "some of this money probably belongs to you. It doesn't matter if you are young or old, male or female, employed or unemployed, black or white, rich or poor, married or single or whatever."

What do you have to do to cash in on this bonanza? "The first thing you need to know," says the text, "is that there are at least 171 perfectly legal ways to get a check out of Uncle Sam." (That came as a surprise to me. I thought there were more than 171.)

The advertisement cites examples. Did "any member of your family" earn less than $8,000 least year? If so, that person "may have a surprise check for $1,000" waiting for him.

Are you retired? "If you know how, you may be able to get $587 extra every month over and above your Social Security check. Nearly 2 million people are doing this right now."

Are you now on Social Security? "With the right information, you may be able to jack up your payments to $848.80 every month just by filling out a simple form."

The ad says it is rather easy to get a chunk of this money that Washington is throwing around by the billions. Some people gets as little as $35 a month, but some of the checks "are for as much as $15,000 or $50,000." Persuasive little teasers follow, e.g.: "In just one U.S. Payment Program 31 million Americans get a check every month. In another, 19 million more get monthly money." Then we're told, "This is not welfare or charity. The government owes you this money." You just have to know how to get your share of it -- and the advertiser offers to tell you exactly how to claim you share. Just fill out the "Government Cash Request Form" and send it in, together with your check for $12.95.

I am almost (but not quite) tempted to send in $12.95 just to find out how much of the information supplied has value and how much of it refers to programs that are already well known to those who qualify -- things like Social Security, Medicare, Medicaid and veterans' benefits. But I just can't bring myself to respond to an ad of this kind.

Perhaps the president, the Congress or the postal inspectors should look into the matter. If there really is an "Amazing Lost Money Secret of the U.S. Government," disclosure of the secret might guide us toward sensible budget cuts. And if there isn't a secret way for anybody to live off the U.S. Treasury, we're eft to wonder why such advertisemnts are sent through the U.S. mails. BARGAIN DAY

Gerald Abel of Fairfax has also sent me an advertisement mailed to him recently. It is from a bank in a small town in California and offers him a Visa card with "no membership fees."

All Gerald needs to do is sign a blank that was enclosed and he will immediately be sent a Visa card and a check for between $500 and $1,800.

A disclosure statement was also enclosed, as required by law. One who takes the trouble to read hundreds of words of small print learns that he will avoid the payment of "membership fees" only if he accepts a loan of from $500 to $1,800 -- at an interest rate of 21 percent. The annual interest rate on $500 at 21 percent is $105.