The manager of Fairfax City, where nine persons have been killed in house fires in the past eight months plans to ask the City Councol to buy 500 smoke detectors to sell to city resident at cost.

All nine victims could have been saved if their homes had been equipped with detectors, city fire officials say.

"The city's simply got to take the initiative," Manager George E. Hubler Jr. said yesterday. "We've got tl take some strong action to prevent such tragedies."

But Hubler's proposal has encountered immediate opposition from the Fairfax City Chamber of Commerce.

"The chamber does not think the city should be competing with city businesses," said Barbara Freson, executive vice president of the group. "We are not opposed to the city encouraging people to buy smoke detectors. We are working with the city on an alternative proposal."

Under the alternative Freson said, the chamber would distribute a brochure on smoke detectors to all 6,7000 residences in the city and set up a speakers' bureau stressing the value of the devices in giving early warning of a fire.

Hubler's proposal will go before a City Council Tuesday that has generally supported the principle that the least government is the best government.

I've got mixed emotions." Mayor Nathaniel F. Young the head of the City Coucil said in an interview. "We should do something obviously . . . The basic thing I wonder about is that we would be setting a precedent. It's very easy to slide into selling this, that and the other."

Young said he would prefer to see the Chamber of Commerce organize a sale at all shops in the city that carry smoke detectors most of which are offered in the $20 to $60 range.

Council member Susanne W. Max said: "I'm not in favor of governmentintrusion in people's lives. But I fell something should be done. If (by using revenue sharing money to buy 500 smoke detectors and selling them to city residents at cost) we alert people to their value, we will be doing a community service."

Under Virginia state law smoke detectors have been required in new townhouses and apartment for which building permits were obtained or after September 1974. The devices have been required in new single family houses under the same conditions since February, 1976.

In Maryland, smoke detectors have been required in all new dwellings since July, 1975. Starting on July 1, 1978, Montgomery County will require them to be installed in all old dwellings as well.

The District of Columbia and Prince George's County local governments are considering legislation similar to the law that goes into effect in Montgomery County next year.

A spokesman for Montgomery's fire prevention service said, "we've had quite a new cases where people's lives have been saved because of smoke detectors. Smoke detectors function by sounding an alarm when the device detects a certain level of smoke in the air.