ITS ROSES, roses, all the way for Dr. Paul Johnstone, who is a sort of grand old man of the Potomac Rose Society; but I was shocked to hear him say that is only since 1941 that he has become a rose addict.

"Like Picasso, I had my Blue Period," he said at a National Arboretum seminar. "I used to grow irises. I was a fanatic for them. Bought all the new kinds from Bolgiano's when they were down on - was it G Street? All the fragrant kinds.

But then the irises only bloom for two weeks or so in May and it pours rain the whole time, and the rest of the year you are cutting out borers and poisoning them to death."

I never heard a more accurate description of the tris grower's lot.

"So I started with roses. First I had a period of columbines, surprisingly enough. Not many people go in heavily for columbines. Then it was pansies, followed by petunias, then chrysanthemums. But at last roses.

"When they asked me to join the Potomac Rose Society, I first told them I didn't join much. I am a member of the American Historical Society and the Episcopal Church, and I figured that was enough things to join."

But he did join the rose society, and is now considered one of the more reasonable rose fanatics around.

He gave us a list of roses he has confidence in, for Washington, with special emphasis on roses that bloom their heads off. There are, as everyone knows, some admirable roses that lack nothing in splendor; "but you are lucky to get a dozen flowers a year from the bush."

Ones he thinks you would like - a free-flowering tribe to which you could add your own lovely sulkers - include:

Garden Party, Royal Highness, Mr. Lincoln, Tropicana, First Prize, Granada, Tiffany, Century II, Chicago Peace and Fragrant Cloud.

Papa Meilland, Peace, Pink Parfait, Confidence, Swarthmore, Michele Meilland (I rather like that one, myself), Mt. Shasta, Aquarius, Red Lion, and John Waterer.

Also Iceberg, Europeans, Redgold, Betty Prior, Coup de Foudre (or Thunderbolt), Lily Marlene, Tomango, Gene Boerner, Orange Sensation, and (his great favorite) Ole.

For cutting, he especially likes Orange Sensation, First Edition, Faberge, Angel Face, Matador, Ice White and Edelweiss.

Now I have always been very honest about irises, my favorite flower, and never deceived anybody about them. They require endless labor in the way of hand weeding, and the best position in the garden, and even then they may rot.

Dr. Johnstone would not mislead a fly, but when he says roses are very easy indeed to grow, he means you resign yourself,of course, to mulching, spraying for blackspot, keeping a sharp eye out for mildew, stem canker, crown gall, etc., etc.

They are every bit as troublesome as irises. But he has one tremendous point that no iris nut can argue with: The roses, unlike the irises, do bloom steadily from the end of April into November. Irises don't.

Of course, a rose is not an iris (as iris fanatics smugly point out); and I don't care what you feel the fool thorny things, they are never going to overwhelm anybody with their massed glory. On the other hand, though I had never thought of it this way before, I suppose you could say an iris is not, after all, a rose.

Decades ago a list of roses for Washington was got up by Whitman Cross, which includes two Climbers that Cross thought superb, 'Mermaid,' and 'Mme, Gregoire Staechelin.'

The first is sulphur-ivory, a single bloom not much good for cutting; and the second, a rich soft pink frilled or ruffled flower, stained crimson outside, superb for cutting but blooming only in the spring for a couple of weeks, and nary a flower the rest of the year.

They were gorgeous in the 1930s, and they are gorgeous now. I know of no climbing roses more exciting, and extremely few as good. It depends, of course, on what you want; but I assume readers have taste as superb as my own, hence I mention these two roses, especially since Dr. Johnstone does not mention any climbers in his list.

I think I hear the swish of bricks coming at me through the air as I now cite 'Radiance,' 'Red Radiance' and 'Mrs. Charles Bell' as three of the 'Radiance' tribe of roses mentioned by Cross 45 years ago, which are still flowers of exceptional merit. I know many gardeners, especially new gardeners and those not really aware of the richness of roses, may not like them.

They are more or less globular, and the reds or pinks of their flowers are soft, not brilliant, and the flowers come with such reliability that perhaps they become a bore after a while. When I was young, I rather looked down on them myself.

I would certainly rather have a bush of 'Radiance' than of 'Tropicana,' and while this is a matter of taste, I think we are somewhat responsible for our taste; and without splitting hairs about it, "Radiance' is the one more likely to be preferred by the best people (i.e., myself). I say this while acknowledging some of my best friends like 'Tropicana.'

Dr. Johnstone's list should be valuable for all who wish to begin with the current favorites, and the two or three I mention from Whitman Cross' odd list might be tried as well (if you can find them) either for eccentricity or (as I could tell you) because for certain qualities they have not really been surpassed or, in the case of 'Mermaid' and the 'Madam,' equaled.