LONDON – Shares in troubled mortgage lender Northern Rock rose on a promise by the central bank to back its deposits, but worried customers continued to line up today to withdraw their savings.

Prime Minister Brown’s government kept up a highly visible effort to calm the panic. Treasury chief Alistair Darling met with leaders of the Bank of England and the Financial Services Authority, and Brown’s spokesman declared that the prime minister had “full confidence” in Bank of England governor Mervyn King.

The central bank announced today that it pumped 4.4 billion pounds ($8.8 billion)— into money markets, in the form of a two-day securities repurchase agreement.

Northern Rock shares rose more than 11 percent at one point before falling back to a 7 percent increase in London. It was a modest gain for the nation’s fifth largest mortgage lender, compared with the two previous trading days that ate away 30 percent of the share price per session.

Mortgage lender Alliance & Leicester, which saw its shares drop 15 percent yesterday, was up 25 percent. Bradford & Bingley, another major mortgage lender, rose in early trading but was down 6 percent at midday following an 11 percent drop a day earlier.

Depositors remained jittery about the bank and the economy. About 50 people were waiting for the Northern Rock branch in Kingston-upon-Thames in southwest London before it opened at 8 a.m.

“I don’t know what we will do with the money yet, but I don’t trust what the government says,” said Doria Watson, waiting in line with her husband. “We were here yesterday but were told we had no chance of getting in, so we are back today and will wait as long as we have to.”

“What the government has said gives us more hope, but there is still doubt and I am not taking any chances,” added Joyce Hutton, who said she had been in line yesterdaybut never got to the door.

Mr. Darling announced late yesterday that the government would guarantee the savings of Northern Rock depositors. Hundreds had ignored earlier pleas for calm and joined long lines outside the branches in Britain and Ireland, seeking to withdraw their funds.

“I do recognize that people are concerned, that’s why we have put the matter beyond all doubt,” Darling said at a news conference after a meeting with American Treasury Secretary Henry Paulson.

Deposits “are safe and are guaranteed, that’s unequivocal,” Mr. Darling added.

“They should have made this announcement on Friday or Saturday,” she Janet Taylor, 63, who was waiting outside a Northern Rock branch in central London. “My confidence is gone.”

Jennie Andrews, 38, a secretary, took her lunch break early to stand in line. She said shortfalls in pension funds and the failure of endowment mortgage plans to perform as advertised had made Britons wary.

“No one has confidence anymore,” Ms. Andrews said.

But the Financial Services Authority said Northern Rock “is solvent, it is not in trouble.”

“We haven’t had a regulatory failure here yet,” said the chief executive of the FSA, Hector Sants. “This bank is solvent and rightly open for business and deposits are safe. The system has worked.”