NVR L.P., the financially troubled McLean home builder, yesterday made official what it has warned of for months, saying it won't make a $14.5 million interest payment on its bonds due today.

In a brief statement, the company also said it has begun discussions with its major bondholders. The announcement signified the onset of what could be make-or-break negotiations between NVR and its creditors at the same time that the company is in critical discussions with its lenders.

Sources familiar with the negotiations said that discussions with the bondholders, who have hired legal and financial advisers, are not expected to begin in earnest until after Jan. 1, when the company is able to turn its attention away from its bankers.

NVR has been in negotiations with its bankers for months, seeking an extension of a $220 million line of credit that funds its operations. That line of credit, lent by a consortium of eight banks, expires next Friday.

Technically, the bondholders could force NVR into bankruptcy on Jan. 15 -- 30 days after the home builder defaults on its interest payments on the two types of bonds it issued in 1987 to help pay for its acquisition of Ryan Homes.

For the time being, however, that scenario is viewed as unlikely. One reason is that NVR's banks have the power to stop interest or principal payments on the bonds. Another reason, securities analysts said, is that home-building companies traditionally do not survive bankruptcy proceedings well because other home builders are able to easily woo away jittery customers. Thus, bondholders could expect to gain little financially from foreclosing on NVR.

Michael J. Cannizzo, NVR's new president of home-building operations, said in a recent newsletter to NVR employees that the company expects negotiations with its bondholders to be lengthy. "Although we expect to make significant progress right away," the newsletter said, "this matter probably will not be resolved until sometime in the second quarter, maybe even sometime in the third or fourth quarter of 1991."

Sources said the big issue will be how much control NVR Chairman Dwight C. Schar and other NVR directors and executives, who own 67 percent of NVR's publicly traded limited partnership shares, are willing to cede to the bondholders in order to save the company.

Analysts said that allowing negotiations to drag on too long risks raising the ire of a few bondholders, who could decide to throw away their economic interest and force the company into bankruptcy.

Meanwhile, NVR is trying to reposition itself in the stagnant Washington area real estate market. It said last month that it has completed the operational restructuring of the company and decided to rid itself or write down its extensive land holdings, which had been draining cash and were proving almost impossible to resell.

Company documents and sources indicate that Schar has realized in recent months that the bulk of his problem is with the company's NVHomes subsidiary.

NVHomes, which grew rapidly in the 1980s by buying land and building the upscale suburban mansions that fed the real estate buying frenzy, was hit hard in the real estate market downturn that has especially devastated sales of expensive houses.

NVR's now-defunct land-development subsidiary took on tens of millions of dollars in debt to buy land for use by NVHomes. Aside from the land owned by its land-development subsidiary, NVR has said it had additional land acquisition and development debt of $98 million at the end of the third quarter. Most of that land was owned by NVHomes, sources familiar with the company said. In all, NVR owned, or controlled through options, about 8,000 lots in the Washington-Baltimore area.

Ryan Homes, on the other hand, was a conservatively run home builder that preferred buying options on land instead of buying the land outright, and it has held up better in the current home-selling slump. NVR acquired Ryan for $360 million in 1986. Ryan builds more modest houses, priced under $200,000, a market segment that hasn't been hit as hard as upscale homes.