THEY'RE USUALLY eye-catchers, bright promotions with sleek images and abracadabra words:

"Come to Esvia. We have magic mountains and silver-sand beaches, shops to die over and night-life that only slows down when you do. For information, write to our national tourist office."

Lately, they've zeroed in at pocket level: Yes, they say, you can eat a three-course meal with wine for $3.50 at a typical inn in Spain, collect travel discounts when in Portugal and see India via "economical package tours."

So would a happy-days-and-nights country mislead you? If you pack up your nitty-gritty questions and send them off to a national tourist office, will you really get back everything you need to know plus, if you ask, a good fix on where the bargains are?

After test-communicating with 19 of them. I'd say that while there are blessed exceptions, you can't positively count on getting much more than you pay for - namely, something comparable to the price of a stamp. Unfortunately, you could get even a bit less on occasion: A little more than a month has passed without so much as a "Hi there" from five of my 19 tourist offices so 45 cents of my $1.71 postage investment may indeed be down the drain.

Of course, a no reply can be telling in its way. Four of the five - Spain, the Bahamas, Jamaica and Puerto Rico - are known as casual countries, and maybe there's just nothing to add. The fifth is the U.S.S.R.

What should you expect from those who do get in touch? Well, initially I had high hopes of learning about all sorts of "best buys," types of budget accommodations, train and bus discounts and multiple-use passes, pointers about food specialties, freehies and the like. I tried to be specific by writing that I planned a two-week stay this summer, that I expected to visit X (usually the capital city), that I was a woman traveling alone and that I hoped to manage on less than $25 a day.

I welcomed all suggestions, particularly on lodging, sightseeing and transportation, I told the tourist offices of Austria, the Bahamas, Belgium, Canada, Denmark, France, Germany, Great Britain, Greece, Hong Kong, India, Italy, Jamaica, Japan, Mexico, Portugal, Puerto Rico, Russia and Spain. I took their U.S. addresses from Rand McNally's Traveler's Almanac, which lists other countries too, of course.

None had any personalized answers to my request, but 14 responded with booklets, lists and pamphlets. I read them carefully and came to a number of conclusions, such as the following.

Most Likely to Succeed: Hong Kong and India were the quickest to answer. Their material arrived just eight days after I wrote.

Information about Austria came on the 13th day, from Britain and Japan on the 14th day. Portugal and Germany clocked in on the 15th day, Belgium on the 16th, Denmark the 17th, Greece and Mexico on the 19th. There was a pregnant pause until the 23rd day, but then Italy was heard from.

Lo and behold, there was also news from Canada on the 28th day and France on the 29th.

I would think that nations seriously courting the tourist trade would realize that potential visitors are easily plucked out from under them by other places and other diversions. I would further think they'd therefore have unbreakable rules about getting material into the hands of requesters within two weeks at the outside. I would think all that - but obviously I would be wrong.

The Chrysler Corp. Prize: This one is so named because it was the Chrysler Corp. that first introduced me to the practice. Writing as a shareholder, I asked the company a specific question and received as the full reply a form letter stating that Chrysler was indeed happy to have heard from me and hoped that any time I had any questions I would write again.

Whoever devised that one is now, I suspect, working for the Mexican National Tourist Office. From them I got some colorful, picture-filled brochures, one of which was actually on Mexico City, the destination I had asked about - but no hotel list, no examples of any prices, no news of special offers or possible cost-cutters. Instead, they sent descriptive material on Acapulco and other newer resorts, plus a general-information folder that closed by saying complete information could be obtained from none other than the Mexican National Tourist Office. Sure it can.

The Scheherazade Award for Stretching Out a Budding Relationship: This one goes to Germany. I was glad to get what they sent, superficially describing Hamburg, but I kept wondering why I should have to write again if I wanted othr publications that were referred to, in particular a cost-cutter booklet titled "Happy Days in Germany," as well as "Where to Go in Hamburg" and "The Hamburg Guide." All three sounded to me much like what I indicated I desired in the first place. In truth, I was also a tiny bit troubled by the hotel guide that arrived. I suppose it's useful to know what Hamburg hotel prices were in August 1976, but I haven't been able to work out why.

The Good TryPrize: To Austria. Their general-information booklet on Vienna is handsome, informative and credits the reader with more than a third-grade level of understanding. It even pokes a little fun at its subject and makes it sound slightly saucy - anything but a dull place to go.

Austria's was also the only tourist office to caution me even obliquely that $25 a day might not leave me in the lap of luxury. Included was list of "moderately priced" Viennese hotels and pensions quoting guideline rates for doubles with bath at $22 to $34, which would normally make it roughly $19 to $28 for singles.

Blue Ribbons: The only birds, India and Hong Kong, won all around. I read with increasing delight tantalizing tidbits as well as hard-headed, nuts-and-bolts advice. At Bhirgu in the Himalayas, the Indians told me, I'd see where the astrologer-hermit ofpes." And around Darjeeling, I could expect to be greetepes." And around Darjeeling, I could expect to be greeted by the locals with a welcome drink called "chhang," brewed from boiled potatoes.

A Hong Kong pamphlet titled "Six Waks" led me through snake shops (snakes venom mixed with Chinese wine makes an expensive but popular winter drink") and streets where shops deal mainly in paper goods ("including kites and specially constructed paper houses and luxury items for the deed"). Quick, Jeeves, my suitcase!

Honorable Mentiona: The British do very well. Their problem is that they have so much to show and tell that they can't get it all to you for free. So they send a book list. So that's not bad. But I still received a large assortment of how-and-where literature, too, as well as "Britain - A Land to Explore," which explains how to get your tax money back when you shop, what taxi rules and rates are, etc.

The Belgians, I thought, were equally forthcoming and interesting. Best of all, their literature was budget-concious and took pains to point out potential savings.

Last and Decidedly Least: The material I got from Denmark and Japan made them sound like "good-for-you cereals. But for overwhelming skill at painting a picture of perfect dullness, I give you Greece. A reader might wind up easily convinced that not much has changed there since the birth of Aphrodite.

I kept at it but found it difficult to keep my eyes from crossing as I read that "life in Mykonos is lunar and flows from one full moon to another, to the tunes of the bouzoukia and to the songs of the Aegean. "I was equally thrilled to learn that at various places there "ample entertainment facilities," that restaurants "abound" and that shops have "almost anything one could ask for." The whole country, I read appears to "favour holidays of long duration." From experience I know that it does - but no thanks, I think, to the Greek Tourist Office. Their brochures could drive you straight to Turkey.

I've mentioned most of what I found exceptionally good and exceptionally bad. There was also the pedestrian. To much in the bad or so-so category was basically bad or so-so because it seemed to have been produced by people who have no comprehension of travel, apart from correctly spelling the word. In a period when sound information is essential, they serve up empty adjectives. In a period when most people are perforce price-conscious, they slide over practical guidelines almost as if it is news unfit to print.

In the end, though, for travelers who don't ordinarily light cigars with dollar bills, national tourist offices are still an information source to tap. Certainly, though, anyone who has a choice between writing or making a personal visit should choose a visit. You can then see for yourself what literature is available and useful (Unfortunately, since many of the offices are headquartered in Manhattan and have no branches elsewhere, that option is not a practical one for most potential travelers.)

At the least such material from the national tourist offices can help you frame your travel questions. At best, it answers them.