On the first day of its national on-air fundraiser, National Public Radio received pledges of $600,000 from its listeners. That support, combined with the expected signing this afternoon of an $8.5 million loan agreement with the Corporation for Public Broadcasting, gives a strong start to the rebuilding of the embattled network.

"The Drive to Survive," the three-day fundraiser that started yesterday, was organized to help the member stations repay some of the debt they have incurred helping NPR out of its financial problems and to give a boost to the network's programming and news divisions. About 100 of NPR's 281 member stations, including WETA-FM but not WAMU-FM in Washington, are participating by running special appeals during the network's award-winning news shows "Morning Edition" and "All Things Considered."

After months of financial uncertainty, NPR averted bankruptcy last week by negotiating an emergency loan from CPB, the independent agency that funnels federal money to public broadcasting. The two parties set today as a deadline for signing the agreement that gives NPR a line of credit up to $8.5 million and forgives $600,000 CPB has already lent the network for debts this year. The finalization also will free an additional $500,000, the second half of NPR's monthly payment from the federal government. The first was released last week to meet NPR's Friday payroll.

The $8.5 million loan will come from CPB's short-term investments, or its "float," said Fred Wacker, CPB vice president of finance. The money, kept by CPB in a bank and gaining interest, has been committed through contracts but not yet disbursed. "NPR will be paying the interest which we would have been earning. For the remainder of the fiscal year, that's 9 1/4 percent," said Wacker.

By 1:30 p.m., after the morning phase of the drive, $281,000 had been pledged. "Everyone is gratified and encouraged," said Jan Hausrath of the NPR public information staff. "We have heard from a good portion of the stations. About $35,000 of that goes to NPR."

The stations in the fund drive have the option to reimburse themselves for any federal funds they have pledged to lend NPR, and then to divide the surplus between the stations and the network. The federal funds lent by the 100 stations, according to Hausrath, total $600,000.

WETA, which does not broadcast "Morning Edition," started its fund-raising during the early evening news show "All Things Considered." As of 7 p.m. last night, it had received $17,693 in pledges. The station has decided to send all the money raised to NPR. "We are giving all of our money to NPR--that is the first thing we want to do," said Kim Hodgson of WETA.

The other local NPR member, WAMU-FM, is not participating, mainly because the plans for its semiannual drive Sept. 24 to Oct. 1 are well under way. "We had pledged our federal community service grant money, and that money is calculated on local listener support. So the more listeners we can cull is of importance to NPR. Our not conducting this fundraiser was a judgment based on how well we could help NPR," said Nina Kern of WAMU.