Poles struggle to 'get by' on $80 a month. Just to fill an average car's gas tank may cost as much as $160

Just how - inquired a visiting friend, staggered by the lowest income levels here - does one ''live'' on $80 a month? Poland is, after all, one of Europe's largest countries, and by no means one of its least economically endowed.

Yet many of its citizens do, in fact, receive just that or little more. How do they manage?

The short answer is, of course, that one doesn't ''live'' on $80. One simply contrives to ''get by.

After a year of steady decline in the Polish currency's purchasing power, $80 is now worth about 8,800 zlotys - at the official rate of $1 to 110 zlotys. On the ''free'' market, a dollar fetches 600 zlotys.

Official findings and statistics vary. But all indicate at least several million Poles are having to subsist on such low incomes.

Consider the price of food: A kilogram loaf of bread costs up to 30 zlotys; one egg, 18 or 20 zlotys; a liter of milk, 14 zlotys; a kilo of sugar and a kilo of flour cost 50 and 30 zlotys, respectively.

That's only a few cents, cheap enough by most standards. But these are Polish standards, Polish incomes and prices.

Reality - the reality of inflation - strikes home when you look at the less basic commodities needed in an ordinarily modest daily diet.

Tomatoes, which were abundant this spring, were still 400 zlotys per kilo at the beginning of June. Cheese - and not very good cheese at that - is upwards of 300 zlotys. Sausage, a favorite food of most Poles, is 400 to 500 zlotys. Cheaper, inferior meat is from 150 to 200 zlotys. (This meat is the only kind most Poles can afford and accounts for most of their monthly ration of 2.5 kilos per person.)

A little extra - such as good quality meat off the ''free'' market for a special occasion - can cost up to 600 or 700 zlotys per kilo. Even with two wage earners each bringing home $80 a month, a family of four doesn't go to the ''free'' market often.

Maria P. is a hotel worker. She has her own flat, which was bought in better days in the '70s. A son, his wife, and their small child share it with her. It has three rooms, itself a luxury for most of today's Poles. But apart from their bathroom and kitchen, their total living space is still only 30 square meters.

Mrs P. makes just a little more than $80. By doing some extra work, like laundry, she brings her monthly income up to 11,000 zlotys ($88), which is as much as her son earns. He is a teacher.

It is one of the extraordinary anomalies of Polish economic management that a job like hers, or an office block cleaner's, pays more than many professional grades, from teachers and hospital interns, to actors and the like.

Mrs. P. worked as a trained nurse until she found she could do better in a hotel. Almost all the combined family income goes for food.

The way prices are now, she says, ''we cannot get by, even on the barest standards, with less than 15,000 zlotys a month for food, and it's still not enough.''

That averages out to 500 zlotys daily. Tomatoes at 400 zlotys a kilo, and a nicer cut of meat at 600 zlotys. . . .

How do they manage?

And what about clothes? Mrs. P. laughs. She explains the system under which people may get loans at their workplaces for clothes or household necessities. Conditions are strict. One loan must be paid off, in monthly installments, before a second can be obtained.

''Before Christmas,'' she says, ''we borrowed 20,000 for clothes. Now we are paying it back, and, when we've done so, we shall need another.''

In ordinary ''public'' shops, a basic suit is 5,000 to 6,000 zlotys, and a summer dress at least 2,500 - ''if you are very lucky,'' says a woman friend. The alternative is to buy ''private'' at twice or more prices ''for something at all nice.''

One Pole in four is said now to have a car. But in these zloty-stretched days , one hears fewer and fewer people even discussing the possibility. Why? Probably because one liter of gasoline costs as much as 435 zlotys ($3.95). Even the young now opt first for an apartment, ''a place of our own.''

Last year, the Warsaw party organization reported, it received nearly 15,000 written and oral complaints. The majority concerned housing.

Next year, after a 10-year wait, Mrs P.'s son and daughter-in-law are to get their own flat. She herself must go on pension, and, if present rates hold, will get perhaps 7,000 zlotys a month.

It is not a prospect she views with equanimity. She would prefer to go on working. ''Compared with many, I have a good job,'' she says reflectively.

Not many Poles are so philosophic and who can blame them?

A year ago, a government probe of everyday living in some 56,000 typical households showed the income of only 2 percent of them matched their needs. No less than 31 percent managed to exist only by buying the cheapest available food and clothing.

Some 2.7 million Poles were said to be living in effect below the subsistence level.

Subsequent surveys have come up with figures demonstating that there has been little or no real improvement. The first alarming reports are emerging about the nutritional effects on school children after years of growing economic hardship. What then does one say of the relative upsurge, though still marginal, of the ''free'' market?

Are the little private shops along a stretch of sidewalk on Marszalkowska street - with lemons and bananas just now at 1,200 and 1,600 zlotys ($11 and $14 ) per kilo - a ''sick'' joke on people who have not seen them for nearly four months?

Or are they symbols of private traders at least serving public needs which the government's markets and shops fail to meet?

Party dogmatists are fulminating about ''fortunes'' allegedly made by private-trade exploiters of consumer shortages. But recent government reports suggested that major graft - unaccounted-for goods, phony bookkeeping, and tax dodging - is really just a fringe of the economy.

An extensive regional inquiry by the Communist Party newspaper, Trybuna Ludu, seemed to come nearer the truth.

Many Poles, it found, regarded talk of huge profits as exaggerated. Local authorities as well as consumers saw ''positive'' aspects in the availability, choice, and quality of goods in the private sector.

A woman was quoted as saying: ''Private shops may be more expensive. But they're the only ones where we can get fashionable clothes and accessories - and without queuing!''

Said another: ''If the state-run clothing industry made a little effort and produced better things, half the private boutiques would quickly go out of business.''

Quite.

Poles don't take tea with milk. They like it with a sliver of lemon. That is why the lemons on Marszalkowska Street the other day seemed to be finding plenty of buyers. Despite the price.

The buyers didn't look particularly well off. They bought only a couple of lemons, or a quarter-kilo. But it still left one (like this writer) who has spent a long time in Warsaw asking the same question as the visitor passing through:

How does Mrs. Maria P. - and the 3 or 4 million other ordinary Poles at the bottom of the heap - really manage?