Channel 4 announced yesterday that Gordon Peterson of Channel 9 will move to the NBC-owned station early in September as co-anchor, with Jim Vance, of the early and late week-night news.

Peterson, a major factor in rival Channel 9's longtime dominance of the local TV news races, would replace Jim Hartz.

However, late yesterday Edwin Pfeiffer, vice president and general manager of WDVM, insisted that the station still has a valid contract with Peterson running through 1982 and "our intention is not to just lay down and accept [the move]. We plan to fight to keep him."

Pfeiffer contends that "we have a personal services contract with Gordon, and it will be our intention to protect our contractual interests. The matter is in the hands of the lawyers.

"gordon is a great asset to us and he's a fine guy. We certainly want Gordon to continue here at Channel 9 -- we think the world of him."

John Rohrbeck, vice president and general manager of WRC-TV, said yesterday that "in the opinion of [Peterson's] counsel and ours, he does not have a contract with WDVM."

As in most TV contract disputes, the issues are quite complex, although basically Peterson feels his contract was with Post-Newsweek Stations, which last year swapped Channel 9 for a Detroit station owned by the Evening News Association, which took over Channel 9 here last July.

WDVM, in turn, feels that Peterson's personal services contract was assigned to them when the station trade was completed.

There is an ironic symmetry to Peterson's surprise move, since it was his teaming up with Max Robinson in 1971 as a co-anchor at Channel 9 that pushed that station into first place in the Washington market news race through most of the '70s-a position long held by Channel 4.

Robinson moved to ABC News last July just as the station changed hands. After some early slippage, the teams of Peterson and Maureen Bunyan in the early evening and Peterson and J. C. Hayward at 11 have stayed number one in the news ratings.

Peterson said yesterday that his decision to move "was not a question of money, it's a chance to spread my wings a little. There have been discussions of some exciting ideas for special programs at Four-speaking directly to the issues that are concerning us all these days. And at WRC we can get on them right away-without having to wait six months for a decision."

If the deal goes through, Peterson will replace Hartz, who has been at Channel 4 since early 1977 under a contract with NBC News. His future with the network is uncertain. Hartz is currently out of town working on a documentary for Channel 4.

Rohrbeck said notifying Hartz of the decision to drop him yesterday "was probably the hardest thing I've ever had to do in this business. He's one of the outstanding newsmen, a true professional and a class guy."

Rohrbeck pointed out that since Hartz had teamed with Vance as co-anchors, the station's news ratings had climbed steadily in the past two years.

Although in the most recent monthly ratings (May), Vance and Hartz were in second place in the early evening and third at 11 o'clock, the pair did manage to increase the news audience over the NBC prime-time leading viewership each night.

Peterson acknowledged that Channel 9's new management "has been in a very difficult position and it's been a tough transition" during the past year.

Late yesterday afternoon, Peterson notified Pfeiffer and news director Milt Weiss of his decision to leave on August 22, giving two weeks' notice that would take effect after a scheduled week of vacation.

Peterson, 41, joined Channel 9 in 1969 after a stint as a radio reporter in Boston and originally covered the anti-war demonstrations here as a reporter before teaming up with Robinson.

WRC's Rohrbeck said yesterday that "for many years Peterson has been a dominant figure in the Washington television market. His many talents as a broadcast journalist, blended with those of Jim Vance, place us in a position of providing the Washington television market with the strongest possible anchor team."

The future makeup of Channel 9's news anchor teams will, of course, depend on the outcome of the pending legal wrangle, and Weiss yesterday declined to speculate on any possible readjustment at Eyewitness News.

NBC News president Lester Crystal was notified of Rohrbeck's decision to drop Hartz yesterday while on business inn Chicago. No decision on Hartz' future will be made until later this month, according to an NBC News source in New York.

Hartz came to Washington under terms of another of those complex TV contracts that paid him $200,000 a year, with portions of the salary paid respectively by the "today Show," which he had previously co-hosted, NBC News and WRC itself.

He was probably the highest-priced news anchor in town.WRC refused yesterday to reveal Peterson's new salary, but one informed source told us yesterday "it's bound to be up there pretty good, and I think Gordon was making around $125,000 a year at WDVM."