Montgomery County Executive Charles W. Gilchrist yesterday said he will veto a bill, passed by his opponents on the County Council, saying it was the "last straw" in a series of council measures designed to wrest control of the county's cable television process from him.

The bill, passed Tuesday, would prohibit citizens who serve on two cable television advisory panels from participating in partisan politics or from holding a county job for 18 months after serving. Although Gilchrist would name panel members, the bill would give the council power to remove any member.

At a luncheon meeting with reporters, Gilchrist used some of the strongest language since his election campaign to rebuke the four-member council majority for what he called "unacceptable legislative game-playing" with the county's cable television franchise.

Council President David L. Scull yesterday called the veto plan "disappointing. The bill assures clean governing of the county's cable TV station. . . . Political cronyism is not our style in Montgomery County."

Gilchrist had opposed the restrictions as too strict because the panels are advisory, with no decision-making power. The veto announcement opened yet another chapter in Gilchrist's power struggle with the Scull-led council. Under Scull, the council has passed a series of measures over Gilchrist's objections while attempting to shift more governmental power to the council.

This will be the first time Gilchrist has resorted to a veto during the battle. His last veto was in September 1981, and it was later overridden. But an override is unlikely this time. Five votes are needed to override a veto, and the three members--all Gilchrist allies--who voted against the bill are unlikely to switch and join the four-member majority.

One of the citizen panels will advise the executive on cable rates and fees. The other will draw up the bylaws for an independent corporation to manage channels reserved for government use. Gilchrist had already submitted the names of 40 citizen volunteers to serve on the two panels, but Scull sent the lists back and introduced a bill with the restrictions.