Ten minutes after she took the phone call, 15-year-old Holly Green was still excited. "The man said he'd like to donate $5,000 to us," reported the D.C. Youth Orchestra's clarinetist. "I couldn't believe it, so I kind of repeated it twice to make sure. Then at the end of the phone call I checked on the amount once again. It sounded too good to be true."

The young musician had reason to be excited. She and 64 other orchestra members are on pins and needles wondering whether a planned concert tour to Europe will be canceled at the last minute because they haven't raised enough money -- $88,000 to be exact. The orchestra has until the end of this week to get the money, and as of Monday, $30,000 still was needed. The members and their leaders were getting tense.

As it turned out, the offer to Green was too good to be true, as orchestra leaders learned the next morning. The unkind hoax occurred during a recent fund-raising radiothon, which raised $11,100 toward the planned tour of Greece and Yugoslavia Aug. 3-23.

Green and several fellow musicians spent that day in the warm Coolidge High School teachers' cafeteria answering phones, taking pledges and hoping for the big donation. The phones are still operating and donations can be made by calling 723-0898.

The young volunteers learned how to urge their callers gently on. "If people pledge $5 or $10, you tell them that if they give $25, they can get a record we made," explained Green.

Unfortunately, when violinist Kimberly Pendergrast tried this tactic on one caller, she found the caller didn't own a record player. "I'm so sorry," said Pendergrast. "So am I," replied the caller.

But most of the calls went without a hitch. "Hello, D.C. Youth Orchestra yradiothon," said violinist Stephen Key, 16, looking cool and professional. "May I take your pledge? You want to give $200? Okay."

"What?" said an unbelieving Green, who had not yet been offered the fake $5,000.

"Tell him about the string quartet -- don't forget," urged Pendergrast.

Her reminder meant that donors who came up with $250 or more were entitled to have a string quartet of Youth Orchestra players at their next party. Martin Rubenstein was one such benefactor.

"We just missed my son's Bar Mitzvah by two months, so we can't take advantage of that opportunity," said Rubenstein. "My daughter's 15, but if we save it for her wedding that would be waiting too long. I know: we'll throw a party at which the quartet will play and it will be a fund-raiser for the D.C. Youth Orchestra."

Among those who had been answering the phone at 7 that morning, when Rubenstein phoned, was orchestra parent Charles Adams.Later in the afternoon Adams was still at it, minding the toops, keeping the tally, dispensing wise counsel.

"Can someone pledge $2 if he says he can't afford any more?" asked Pendergrast. "Sure," Adams answered. Rome wasn't built in a day.

No one every claimed that raising money to send a youth orchestra to Europe is easy. Orchestra parents have paid whatever they can toward the trip, which will include concerts in several Green and Yugoslavian cities and an appearance at a festival in the Yugoslavian city of Dubrovnik. Donations have added more. A raffle helped, as did a Capital Children's Museum benefit last Sunday. T-shirts, buttons and tote bags are being hawked busily. Churches pass the hat after concerts.

Still, $88,000 is a lot of money. "I'd like to sleep nights," said Lyn McLain, orchestra founder and conductor, pacing as he spoke. "I want these kids to go and it's a vare, no-nonsense fact that the trip might be canceled if we can't pay for it. At least they are doing a beautiful job on the phones. I'm like a fish out of water, though. Although the first pledge I took was from an old friend and another was from a student of mine, I figured I'd better stop after that. Other people do it better."

Stephen Key, who travels 40 minutes each way from Landover, Md., to orchestra rehearsals at Coolidge, pondered the coming trip. "Just about everybody's going except for a few who had other things to do or didn't want to go," said Key. "Can you imagine not wanting to go?"

The 65-member orchestra, which celebrated its 20th anniversary this spring, has members ranging in age from 11 to 19. It performs about 50 times a year at places like the RFK Stadium and George Washington University. In anticipation of raising the money needed for the European trip, a farewell concert is planned for 8 p.m. Tuesday at the Washington Cathedral, where the orchestra will play the same songs planned for its European audiences. The concert is free.

The youth orchestra includes the "crowned jewels" of a music program that involves 800 students and six performing groups. Funded primarily by the D.C. Public Schools, it operates with an estimated $350,000 budget and a staff of about 50 part-time instructors plus administrators and support personnel.

Most of the participants are from the District -- about 88 percent -- but the program also accepts students from Virginia and Maryland. It is a free program, except for a $15 instrument maintenance fee, aimed at teaching music to students regardless of whether their parents can afford the lessons. But there are no income guidelines in order to get in, according to Sara Green, concert manager.The only limitations are those of age -- you must be at least 7 years old to start learning an instrument.

The free music lessons range from beginning through advanced levels and students can play in various ensembles; the cream of the crop join the Youth Orchestra. In the past, the orchestra has traveled to Switzerland, Germany, England, Scotland and Japan.

"Please keep those phones ringing," intoned the announces from WGMS, the AM-FM fine arts station that sponsored the radiothon. "We have a total of $65 toward this $1,000 we are trying to match. Don't give up. There are 10 phones down there; I'm occupying one of them, but there are nine left."

At that moment, all of those nine seemed to jangle at once. One young musician groaned, another made a face, but they kept up with the demand. "I couldn't write fast enough, but we got the money somehow," announced Green when the spurt was over.

Mothers and siblings chipped in with radiothon pledges that afternoon. Two people called string bassist Jon Poindexter asking to have their televisions repaired. Pendergrast was beset by a little girl who kept phoning back with different names and addresses.

"Be sure to take their names," pleaded McLain, noting that "No Name" was scrawled on a couple of slips. "I mean, I could sit over there and call you all day, not giving my name, and end up sending you nothing." He was assured by his crew that although the anonymous callers had asked to stay anonymous, there was no reason to believe they would welsh on the deal. He then retired to a corner seat near the radio and sat there looking worried.

By the end of the radiothon late that night, after hearing the final tally, McLain didn't look quite as worried. Poindexter ended up hungry, since he hadn't brought any lunch, but still enthusiastic. Rubenstein ended up with the promise of some early Haydn and Mozart quartets to adorn his party. And the orchestra is getting closer and closer to Europe.

(donations also may be sent to P.O. Box 4898, Cleveland Park Station, Washington, D.C. 20008.) CAPTION: Picture 1, Holly Green, 15, and Kimberly Pendergrast, 15, hope each call brings a big donation to the orchestra; Picture 2, Members of the Youth Orchestra get ready to take phone calls during a recent radio telethon, Holly Green, 15; Kimberly Pendergrast, 15; Stephen Key, 16; and Jon Poindexter, 14. The telethon raised $11,000 for the group; Picture 3, Lyn McLain, conductor of the D.C. Youth Orchestra, listens anxiously to the radio during a recent telethon to raise money for a planned concert tour in Europe. Photos by Lisa Berg for The Washington Post