150 years ago, a teen-age princess became Queen Victoria. From Cornwall to Scotland, Britons are flocking to Osborne House to celebrate her accession.

IF you did not know that 150 years have passed since Queen Victoria inherited the British throne from her uncle, King William IV, you may be forgiven. Compared to the Queen's Golden Jubilee of 1887 and the Diamond Jubilee in 1897 - both of which were celebrated with great pomp and circumstance - this anniversary might seem scarcely worth raising an eyebrow. But the 150-year mark falls at just the right moment: After all, interest in the Queen and the achievements of her long reign has in recent years emerged from the unfashionable gloom.

The modest celebrations around the country are centered on the Queen's private home, Osborne House, on the Isle of Wight. The state apartments of the house have been open to the public since 1904, but it is not until recent years that the house has become popular with visitors, many of whom come especially to see the private apartments. Seldom does the public have the opportunity to peer into the off-duty lives of British monarchs, to wander round their private rooms and examine their possessions. This is precisely what a visit to Osborne provides.

Victoria received the news of her uncle's death early on the morning of June 20, 1837, at her London home, Kensington Palace. She was barely 18 years old. Less than three years later she proposed marriage to her German cousin, ``My dearest, dearest, dear'' Albert of Saxe-Coburg and Gotha. Princess Victoria, the Princess Royal, was born later that year, the first of their nine children.

Five years later the growing family found itself in need of larger quarters. Windsor had no private garden and Buckingham Palace, although recently much enlarged, suffered from a ``total want of accommodation for our little family, which is fast growing up.'' The Queen and the Prince wished to have a private home where the children could learn their lessons and enjoy life free from the constraints of their official roles. They could have moved into the ``Marine Pavillion'' at Brighton, which the Queen had inherited from George IV. But it was unlikely that this extravagance of chinoiserie on the Sussex coast would suit the ``little family.'' It didn't and was sold. Then, on May 1, 1845, the Queen bought the 450-acre Osborne estate, upon which stood a Georgian house. The Queen wrote that it was ``impossible to imagine a prettier spot - valleys and woods which would be beautiful anywhere; but all this near the sea ... is quite perfection; we have a charming beach quite to ourselves. The sea was so blue and calm that the Prince said it was like Naples.''

In June of that year the Queen laid the foundation stone of a new house that was to replace the old mansion. The royal couple decided not to employ an architect. Instead, the Prince himself designed the house in the style of an Italian villa, as an extension of his original impression of the place. Keen to use the latest building techniques, the Prince had the house built as near as possible to being fireproof: It had solid floors on the ground level and cast-iron girders supported on brick arches. Central heating was provided through hot-air ducts. They soon added another wing, followed by a large double wing to house the retinue. Gardens were laid out with terraces overlooking the sea, and the estate slowly increased to 2,000 acres through purchases.

The interior is large and comfortable, but not palatial. Indeed, were it not for a few outstanding items in the state apartments - ceremonial gifts such as massive porcelain vases from the Czar of Russia and the Emperor of Prussia - this could be the home of any well-to-do couple of the time. Family portraits abound and the furniture is almost entirely British. Apart from the Prince's collection of Italian primitive paintings, everything was modern. Personal touches are everywhere: The hall is lined with bronze statues by Barbedienne, the Parisian founder whose works the Queen and her husband gave to each other at Christmas and birthdays. A rosewood cabinet is mounted with miniature portraits of their children. The drawing room features marble statues of the royal children.

Although the family spent many long holidays at Osborne, the Prince ensured that these were not wasted in frivolous amusements. A Swiss chalet was brought in sections from Switzerland in 1853-54 and erected half a mile from the house. Here the princes learned carpentry and gardening. (In 1860 Prince Arthur constructed a miniature fortress with earthwork fortifications and a tiny brick barracks - excellent training for a future field marshal!) The princesses learned cooking and housekeeping here. The little Swiss Cottage Museum nearby housed the childrens' collections of minerals, fabrics, and curiosities. These are not to be missed.

Nor should one miss the Queen's bathing machine.

On the untimely death of the Prince on Dec. 14, 1861, Queen Victoria fled to Osborne instead of waiting in London for the funeral. Records show that she spent at least two holidays there each year for the next 40 years - more time than she passed at Buckingham Palace. After the Prince's death, the Queen would have nothing altered. With one exception - the elaborate Durbar Room, which was created in 1876 when Queen Victoria became Empress of India - all the rooms now open to the public are much as they appeared in the 1860s.