It seemed like a generous proposal. Warner Amex Cable Communications, Reston's cable TV operator, said it would pick up the tab for last night's homecoming dinner for former hostate John Graves.

But according to some accounts, the politics of cable TV bidding in Fairfax County took precedence over Reston's all-day celebration for one of its best-known residents.

Mona Head, chairman of the homecoming celebration, said Warner Amex officials, after agreeing to pick up the cost of the $15-a-plate dinner and open bar for 150 people, told her the woman she had picked as master of ceremonies would have to go. The reason: the woman's husband was connected with a Warner competitor.

Head's choice for master of ceremonies was Ann Page, a Reston civic leader who is the wife of Rodney F. Page, former chairman of the county School Board and an investor in Trans County Cable Communication Inc., a Storer Broadcasting Co. subsidiary that also is seeking the potentially lucrative Fairfax franchise.

Head said she was told directly by Warner vice president Steven M. Saferin that Page was "unacceptable" and that it would be a conflict of interest if she were part of the program. "I was surprised," Head said. "I didn't think the dinner was a political event." Chosen instead was the Rev. Douglas Ibach, a Reston minister who hosts a religious program on the local Warner franchise.

Reached last night, Saferin denied Head's assertions "unequivocally," calling her account "absolutely not true." Saferin said he had no personal knowledge of the selection process and that Warner Amex had no control over who was chosen.

Since it began competing for the Fairfax franchise, Warner has introduced an improved service in Reston, its local base, and begun sending to subscribers a handsomely printed weekly TV guide free of charge.

The current issue of the guide includes a color portrait of the Graves family.