The Smithsonian Institution's National Portrait Gallery, faced with a public outcry in Boston over its $5-million attempt to remove Gilbert Stuart's portraits of George and Martha Washington to Washington, has backed off.

Both the Portrait Gallery, would-be buyer of the two unfinished paintings, and the Athenaeum, a private Boston library which owns them and badly needs the money, have agreed to suspend negotiations until the end of this year.

The suspension is designed to give the citizens of Massachusetts a chance to come up with the cash to keep the portraits in Boston. A fund-raising campaign, called S.O.S. (Save Our Stuarts), led by Boston Mayor Kevin White and Sen. Edward M. Kennedy is already under way.

Art lovers of the Commonwealth and children alike have been asked to send their checks and pennies to the Boston Museum of Fine Arts, where the Stuart icons have been on view, on loan, since 1876.

"We are still determined to sell them," said Augustus Peabody Loring, the Athenaeum's treasurer. "The price is still $5 million. If the Boston Museum doesn't come up with the scratch, we'll go back to talk to the Smithsonian Institution."

Mayor White, who has compared the proposed transaction to "the Louvre trying to sell the Mona Lisa to the Arabs," had sued to stop the sale. A city attorney said the suit now will probably be dropped.

White's press secretary, George Regan, said last night the "although the mayor will do everything in his power to save our Stuarts, no city funds will be used for their purchase. No state funds will be used either. It's up to the private citizens of Massachusetts."

After 14 months, negotiators for the Portrait Gallery, the Athenaeum, and the museum of Fine Arts, hammered out a deal whereby the paintings, though owned by the Smithsonian, would have been loaned to Massachusetts one year in five for the next 50 years.

Fourt years ago, Loring said, "The paintings were offered to the Boston Museum for $1,633,334. They did not see how they could come up with the money. They turned the offer down."

The proposed sale to the Washington gallery generated dismay among Massachusetts art lovers, patriots and politicians.

"Under the circumstances we have agreed it is only fair to give them one more chance," said Charles Blitzer, the Smithsonian's secretary for history and art. "They have until the end of the year. If they fail, we think the paintings belong here."

In the lamp-lit rooms of the Athenaeum on Beacon Hill, there is some question about the sincerity of the hubbub over the potential loss of George and Martha.

"The general consensus in the reading rooms is that this is a tempest in a teapot," said an Athenaeum staff member. "The paintings are nice and they'll be appreciated wherever they land."

"Really," said one older man, whose annual $300 fee entitles him to membership in the private library, "I think most of the city has never seen them and would never miss them."

Whether it is the loss of art or the cultural intrusion of the nation's capital, the general public has responded to the outcry from civic leaders.

"The switchboard has been blowing up all day," said Joseph Savage, a spokesman for Mayor White. "Hundreds of people are calling, wanting to know where to send their checks to save our Stuarts."