Some guys just can't stop griping about their mothers, but not Glenn D. Lowry, the young curator of Near Eastern art for the Freer Gallery and the Smithsonian's Arthur M. Sackler Gallery, now under construction near the Mall.

"It was mother that did it," he announced with glee yesterday when asked how he found the precious Vever collection of Persian art. The Smithsonian agreed yesterday to purchase the collection for $7 million.

The Vever hoard was the most valuable collection of Persian art in private hands, with a towering reputation fueled all the more by the fact that for the last 40 years it had, so far as scholars knew, disappeared without a trace after the death of its owner, 89-year old jeweler Henri Vever.

Disappeared, that is, until one evening late in November of 1984 in Paris, when Laure Lowry of Williamstown, Mass., sat down at a dinner party and started talking -- as mothers are wont to do -- about her son and his work in Near Eastern art. Her dinner companion, as dinner companions are wont to do, said he too had an interest in the subject and began describing his collection.

Laure Lowry, no expert herself, paid careful attention, and on her return to the United States she called her son to tell him what she had been told. It was, to an expert in Persian art, an event of the quiet, staggering impact, something like breaking the atom must have been to a nuclear physicist. For as his mother went on, it became clear that she, over dinner and wine, had found the Vever collection.

As Milo Beach, assistant director of the Sackler Gallery, remarked yesterday after the signing, "This is not the sort of thing that happens everyday."

Henri Vever's collection -- mostly of texts and illustrations, 461 items all told -- was of such importance to Lowry and Beach that several years ago, when they sat down to make out a wish list for the new museum of Asian art, the Vever collection was number one on it. But they weren't sure it existed. They had no idea where to look. And even if they found it, they didn't know whether they would have the money to buy it. Even if the owner would sell. Little could they have realized that the owner, who declines to be identified but whose American lawyer identifies the owner as a Vever heir, had the stuff stored in New York, where it had been taken 40 years ago as protection against the Nazi occupiers of France.

Why all the secrecy over the years? "Well," Beach said, "I've been wondering about that from the beginning. They seemed to be sitting on it as a sort of nest egg." Many experts feared that the Vever collection was gone, but Lowry and Beach said that several years ago they became convinced it existed when some Japanese art that belonged to Vever went up for auction in London.

Vever's Persian art increases by roughly 50 percent the holdings of the Sackler Gallery, which will open in May 1987 and which was planned around an initial gift of 1,000 Asian works from its principal benefactor, New York research psychiatrist Dr. Arthur M. Sackler. Sackler also made a large but unspecified donation toward purchase of the Vever collection and was active in raising some of the other money, according to Smithsonian spokesmen.

"Every day you tend to pinch yourself about it," Sackler said yesterday in an interview. "Today you could wake up and realize it is not a dream, but reality . . . Just as a physician cannot put a price on life, so you cannot put a price on these objects.

"I think the real credit in this case should go to the staff. This is a glorious enhancement of America's cultural patrimony . . .

"I think the art scene here in Washington in 50 years is going to be as important in the arts world as London or Paris or Rome," Sackler added.

Smithsonian Secretary Robert M. Adams yesterday hailed the acquisition as "perhaps the most significant purchase in the history of the Smithsonian."

After the tip from Lowry's mother, he recalled, "Milo and I drafted a letter to the owner. We met in early 1985. The owner had not intended to sell at that time, but finally agreed to an inventory and an appraisal. We finally saw the collection in February. It was staggering, full of new material that we didn't know about." Major parts of the collection have never been publicly displayed.

In April, Adams went to London to see the collection, where it had been taken for appraisal. Then Sackler also went to London, "and became very enthusiastic," Beach said.

Meanwhile, secrecy had to be preserved, out of fear that another museum would thwart their efforts. And in fact, they said, there later occurred some bidding competition from museums they would not name.

The Vever objects will not go on display until the Sackler Gallery opens, but they are already here and 22 were brought out yesterday for members of the staff and others.

Among the particular gems:

*Eight illustrated pages from the Demotte "Shahnameh" (circa 1330), among the earliest surviving manuscripts of Persian painting. No other collection has so many, and when combined with the Freer's six additional ones, the Smithsonian's holding becomes unique.

*Five illustrated pages from the "Falnameh" (Book of Omens) (circa 1550), which are, for their scale, unique among Persian paintings.

*Eight illustrated pages from "Album of Shah Jahan" (circa 1650), who built the Taj Mahal.

*An "Enthronement Scene" by Abid (dated 1628-1629), a history of Shah Jahan's reign, now in the collection at Windsor Castle.

And what will be Laure Lowry's reward for uncovering the Vever collection? "Eternal gratitude," her son blurted passionately.