For the royal wedding festivities in London, First Lady Nancy Reagan took with her hundreds of thousands of dollars worth of diamonds and rubies and sapphires loaned or sold to her over the past four years by Bulgari, an international jewelry firm, according to Susan Meyer, a spokesman for Bulgari, who has been a personal friend of Mrs. Reagan since the late 1960s.

Meyer confirmed yesterday that the president's wife has had an arrangement at Bulgari since before she became first lady, which has allowed her to choose valuable gems that are "hers to wear as long as she wants to wear them."

Meyer, a West Coast publicist and the Beverly Hills representative for Bulgari, said yesterday in a telephone interview from Los Angeles that Mrs. Reagan had taken several pieces of Bulgari jewelry to England for the wedding including:

A "most incredible pareur " (matched set) of diamond and ruby necklace, earrings, and rings.

A pearl choker centered with a large carnelian intaglio, dating from the 2nd century A.D.

A long necklace and matching earrings of pastel sapphires which Mrs. Reagan had chosen before packing for her trip.

Heavy diamond earrings.

The diamond earrings, Meyer said, were the impressive ones Mrs. Reagan wore in London -- so impressive that reporters covering her visit to England made a point of yelling out past her security guards to ask, "Are those real?"

Mrs. Reagan, according to one account, grinned and waved her fingers and replied, "I'll never tell."

Reached in London last night, Sheila Tate, the first lady's spokes-woman, said she didn't know anything about jewelry or about any loan arrangement. Tate said Mrs. Reagan was at a dinner dance and there was no way to talk to her about the jewelry she took with her to wear at the royal wedding festivities until today, when they would be returning to Washington.

Richard Storm, the general manager of Bulgari in America, said he didn't want to comment because Mrs. Reagan is in London. "Naturally we wanted to check with the White House that everyone is in agreement on this. All we can say is some of the jewelry is ours and some belongs to her. She owns some and some is loaned." Later in the telephone conversation, Storm said he couldn't comment on the wedding and whether or not Mrs. Reagan was wearing any of the loaned jewelry. Storm suggested checking with Meyer about the London jewelry. "As publicist and Nancy's friend she knows better about that," he said.

When it was first learned from a source in London yesterday that the diamond earrings and other unspecified jewelry worn by Mrs. Reagan since her arrival in England had come from Bulgari, Meyer at first acknowledged the firm's general arrangement with the president's wife, but later declined to give specifics. Storm also declined to comment on the loan arrangement with Mrs. Reagan or other customers. He said it is not unusual for Bulgari to have loan arrangements with "well-known" customers. "It depends on the customer, what kind of loan arrangement we have," he said. "Sometimes they are wearing it to see if they like it" or if, for example, "it matches their eyes."

Meyer, who said she has been a close personal friend of Nancy Reagan for 14 years, has made "several trips to Washington" since the inauguration to allow the first lady to choose "whatever she likes" to wear "for as long as she wants to wear them."

Nancy Reagan, Meyer said, "was one of my first friends after I moved to this city [Los Angeles]. She has been wonderful to me."

She added: "I do think she is always so beautiful . . . so elegant . . . our jewelry accentuates that beauty and elegance."

Later she added: "She is a good model for us."

After first promising to make available color slides and black-and-white photos of all the jewelry that Bulgari has supplied Mrs. Reagan, Meyer began to have second thoughts about "an intrusion into her privacy. I don't think I ought to say anything while she is in London and I can't talk with her," Meyer said.

During the course of several telephone conversations yesterday, Meyer asked if "you have to discuss ownership."

"This is just a fashion story isn't it?" she asked. "I will get in a lot of trouble and so will Bulgari if you discuss ownership."

She declined to spell out Bulgari's exact arrangement with Mrs. Reagan.

"Some of it [the jewelry] she has purchased," Meyer said. She added that some jewelry was provided to Mrs. Reagan before she became first lady, but Meyer said, it would be "disastrous" for her to be more specific about when -- or whether -- Mrs. Reagan is expected to return the jewelry to Bulgari.

"There's no question of this being a lend-lease kind of arrangement . . ." she said. "It's fine to say it's hers. Indeed, it is hers . . . there's no timetable for her to give it back . . . She's a classy lady . . . Bulgari's a classy operation."

Storm confirmed that "Mrs. Reagan owns Bulgari jewelry and also has been loaned jewelry on previous occasions," but emphasized he would not comment on the London trip.

Meyer pointed out that "Grace Kelly owns Bulgari [jewelry]," but added that how the princess acquired it "is not really discussed."

Meyher said she took Nicola Bulgari, who heads the family's North American operation, to the Reagans' Pacific Palisades home with his wife, Anna, four years ago "to meet Mrs. Reagan."

At that time Mrs. Reagan acquired a gold coin neclace and a Bulgari watch which Meyer said were gifts and are "hers."

Meyer said that Mrs. Reagan also owns a gold choker centered with a large sapphire "which she usually wears with an open shirt and another long, gold Bulgari chain."

Mrs. Reagan's favorite Bulgari jewels, Meyer said, are the set of rubies and diamonds which Meyer said were completed att the time of the inauguration but not delivered to the White House until "48 hours before the attempted assassination of President Reagan."

Mrs. Reagan, Meyer said, had already worn the rubies and diamonds once in Washington with a red Bill Blass dress.