The Bush administration is giving “serious consideration” to sweetening a $1.2 billion loan offer to the United Nations for renovation of the world body’s Turtle Bay headquarters, U.N. and American officials said yesterday.

The administration and Congress approved the current offer – a 30-year loan at 5.54% annual interest – last fall. That offer carried an expiration date of September 30, putting pressure on the United Nations to make key decisions about its Capital Master Plan in coming weeks.

In particular, the United Nations must decide how it will finance the renovation and where it will house temporary offices during the renovation, after the New York State Legislature blocked, for the time being, U.N. attempts to erect a new “swing space” tower over a neighboring city playground.

Although Secretary-General Annan recommended this spring that the General Assembly accept the loan offer, several member states expressed profound disappointment and marked irritation that the loan was not offered interest-free.

In today’s meeting of a U.N. budget group, the Fifth Committee, it is expected that Washington will grant the world body a reprieve of another year in which to continue deliberation on its financing options.

The Swiss representative on the committee, Anja Zobrist Rentenaar, told The New York Sun yesterday that representatives of America’s U.N. mission informed the Fifth Committee that a new loan offer would be forthcoming. “We don’t have anything in writing,” she cautioned, saying America was suggesting the amount of the loan offer would remain constant at $1.2 billion but there would be “a new deadline and possibly lower interest.”

“It gives us a bit more time to look at the picture in its entirety,” Ms. Zobrist said. A spokeswoman for the American mission, Monica Cummings, said: “We’ve been looking at that option. It’s under serious consideration. We’re still awaiting final instructions from Washington.” The required approval, Ms. Cummings said, would be issued by the State Department.

Ms. Zobrist said the reprieve meant the world body would probably revisit the matter of the loan offer in late November or early December.

That is also when the United Nations is expected to reach some conclusions about where it will house offices temporarily during the renovation, which, according to current plans, are expected to begin in 2007 and take five years to complete, the chief of administration for the Office of the Capital Master Plan, Vivian van de Perre, said.

She said the office had to report to the General Assembly on options for swing space by the end of the year.

The organization was reportedly seeking to rent around 700,000 square feet of contiguous office space, with a large conference facility for meetings of the General Assembly, somewhere in the city. In conjunction with the real estate broker Newmark, the United Nations had identified more than 100 sites, U.N. officials said in the spring, including especially promising ones in Brooklyn and Midtown Manhattan.

The world body had seized on one complex that, because of its proximity to the Turtle Bay campus, held special appeal. Ms. van de Perre said the United Nations had been considering a space on Lexington Avenue – which press accounts have identified as the building at 485 Lexington, near 47th Street.

“But New York City counterterrorism advised against having the U.N. in one building,” citing the security concerns of having an identified terrorist target occupy a standard commercial building close to the street, Ms. van de Perre said.

Ms. van de Perre said the United Nations was looking to separate its various programs and departments and house them in smaller units of commercial space scattered through the city. The option of moving some programs to U.N. cities abroad, too, remained a viable option, she said.

Those comments come amid speculation that the world body may seek to keep costs down by avoiding the option of significant swing space entirely. Citing concerns about asbestos and other safety hazards, U.N. officials decided to vacate the premises entirely and renovate the entire compound at once. Earlier proposals, however, recommended doing the renovations piecemeal – refurbishing the Secretariat building, for example, a few floors at a time.

The U.N. undersecretary-general for management, Christopher Burnham, declined to comment yesterday on specifics of the Capital Master Plan. Mr. Burnham, an American who is expected to oversee a significant component of the renovation, said he has “asked for a top-to-bottom review of every assumption I inherited on the Capital Master Plan.” Those revised assumptions, he said, would include the cost of the project, currently set at $1.2 billion. Mr. Burnham said 60% of the design work has been completed, “which gives us the opportunity to validate the overall costs and scope of the project to a much more definitive degree.” Mr. Burnham, who is a former Connecticut state treasurer, said he would have the revised cost numbers “within weeks.”

Meanwhile, some advocates of the plan to erect a 35-story, 900,000-square-foot expansion tower at the city’s Robert Moses Playground are refusing to let the project die. One leading opponent of the project in the State Senate, Martin Golden, Republican of Brooklyn, said he had been felt out earlier this week by representatives of the United Nations Development Corporation, a city-state entity, about whether his opposition remained unabated. The State Senate is scheduled to have a special session on September 20. Mr. Golden and other Albany lawmakers maintained yesterday that the expansion project was “not happening.”