AUCTIONS

By Rita Reif

Published: April 10, 1987 nytimes

ROBERT DE BELDER, a retired diamond dealer who lives near Antwerp, Belgium, assembled over 30 years one of the finest collections of botanical color-plate books in private hands -holdings that Sotheby's in London is to auction April 27 and 28. The 388 volumes include many of the monuments of botanical illustration, dating from 1600 to 1900, that document the evolution of botanical art. Sotheby's expects the sale to total $4 million to $4.5 million.

William P. Watson, the botanical-book specialist of the London rare-book dealer that helped form the collection, Bernard Quaritch Ltd., said this week that Mr. de Belder's library was the finest to be auctioned over the last 200 years. ''Single-handedly and single-mindedly, he created the greatest private collection of botanical books in the world,'' Mr. Watson said. ''Obviously it is in the top 10 of all botanical-book collections.'' Mr. de Belder acquired major segments of some of the most important botanical-book collections dispersed over the last decade, including the Massachusetts Horticultural Society Library, the Horticultural Society of New York's holdings and the Liechtenstein-based Arpad Plesch Collection.

Mr. de Belder's horticultural interests are wide-ranging and his library reflects this, Mr. Watson said. The collector is a vice president of the Royal Horticultural Society of London and the owner of Kalmthout, a mid-19th-century arboretum 15 miles north of Antwerp that he restored in the 1950's and opened to the public about 20 years ago. ''Books were never a mere antiquarian pursuit,'' Mr. Watson said. ''The documentation of plant discoveries and their pictorial record, often of rare or vanished species or varieties, helped in the development of his botanical garden.'' He explained that Mr. de Belder had used the early records and illustrations to spur horto-archeological recovery and the documentation of lost plants.

The de Belder collection had been offered in its entirety by Quaritch until recently. ''We had tried to sell it en bloc a couple of years ago and failed,'' said Nicholas Poole-Wilson of Quaritch, adding that since the owner needed to raise the money, he decided to sell the collection at auction.

The collection includes most of the major books of this genre produced over a 300-year period. Outstanding among them are Basilius Besler's ''Hortus Eystettensis'' from 1613, which Sotheby's expects to bring from $300,000 to $450,000, and Pierre Joseph Redoute's ''Roses,'' from 1817-24, a volume inscribed by the artist, that may sell for up to $110,000.

Redoute's first botanical illustrations are contained in another volume - ''Stirpes Novae'' by Charles Louis L'Heritier de Brutelle, from 1784. This copy, 1 of 10 known that includes two states of the illustrations - one with no color and the other with color - once belonged to George Spencer, fourth Duke of Marlborough. The presale estimate is up to $120,000. The Austrian Imperial copy of Baron Friederich Wilhelm Heinrich von Humboldt's ''Voyage aux Regions Equionoctiales du Nouveau Continent,'' published in Paris between 1808 and 1829 - a 15-volume work reporting Humboldt's research from his travels through Central and South America - may sell for up for $70,000.

The sale represents about one-tenth of the titles in the de Belder library, Mr. Watson said. He added that no decision had been made about the fate of the rest of the books in the library, which focus on herbal and pharmacopeia medicine and botany. Souvenirs Of the Titanic

Memorabilia of the liner Titanic will be auctioned Wednesday in London, on the 75th anniversary of the ship's sinking. The sale, organized by Onslow Auctions Ltd., a three-year-old firm specializing in sales of transportation-related materials, will be held at the Park Lane Hotel. Among the 45 offerings are mostly Titanic ephemera - letters written aboard on Titanic stationery, tickets of admission to a viewing of the ship, sheet music, a poster and several unused period postcards of the Titanic.

The most important offering is a longitudinal sectioned plan of the ship prepared by White Star Line's Naval Architects Department for the official English inquiry that followed the 1912 disaster. A director and part-owner of Onslow, John Jenkins, said the plan - which measures 30 feet long and almost 5 feet high - was owned by a collector whose identity has not been revealed. The collector had salvaged it in the 1950's from a pile of papers being discarded at the Liverpool offices of White Star's successor, Cunard Lines. The plan is inscribed: ''Titanic plan and section used at the Inquiry. Not to be destroyed.'' Mr. Jenkins said it may sell for $20,000 to $37,500. The rest of the items are estimated to bring from $60 to $15,000 each. Rare Posters By Ricordi

Italian posters printed between 1890 and 1930 by the House of Ricordi, the Milan music publisher, are among the more unusual offerings in Jack Rennert's poster auction to be held May 3 at the Essex House, 160 Central Park South. Mr. Rennert said the Italians never suffered from postermania - which is why there are more French posters than Italian lithographed advertisements for Puccini operas, the Mele department store in Naples and Pirelli tires. There are posters by Marcello Dudovich (the best are the Mele fashion posters), Adolfo Hohenstein (his 1899 ''Tosca'' poster is a favorite among opera buffs) and Leopoldo Metlicovitz (his ''Manon Lescaut'' from 1900 is charming). The 92 Ricordi posters range from $600 to $5,000 each.

A. M. Cassandre is represented with compelling Cubist-inspired posters of the 1920's that include a London poster in red, white, blue and black, showing the hull and stacks of a steamship against the sky (up to $5,000), and an LMS poster for the London Midland and Scottish Railways - depicting railroad tracks and a switch (up to $3,500).

Other poster designers are represented with some of their classics. James Montgomery Flagg's 1917 Uncle Sam recruiting poster, ''I Want You for U.S. Army,'' may bring up to $1,500; Charles Kiffer's 1937 ''Maurice Chevalier'' poster for RCA Records, up to $2,000, and Theophile-Alexandre Steinlen's ''Tournee du Chat Noir'' (1896), up to $4,000.