The Promenade Apartments sit sedately off Wisconsin Avenue in Bethesda, 1,100 units of luxury housing complete with swimming pools, tennis courts, and a Beverly Hills rococo interior of gilded mirrors and chandeliers.

In the great conversion war of Montgomery County, it is the newest battleground.

Last week, after weeks of rumors, the Promenade's affluent tenants found out their building was going co-op -- and ever since things haven't been the same:

Tenants pledged more than $50,000 in legal fees, County Executive Charles Gilchrist went to court to try to bar any sales of co-ops, and around the pools and in the hallways there are vows of a fight to the finish.

"There will be no stones left unturned," vows Jim Nickelsporn, the tenant association president. "We are people of intellect and means and we will use any vehicle we can to stop the conversion."

At issue is an attempt by American Invsco, one of the nation's largest apartment house owners, to turn Montgomery County's strict condominium conversion restrictions on their backs. Instead of selling individual apartments, the new owners want to turn the Promenade into the county's second co-op.

By creating a cooperative, rather than selling condominiums, it appeared initially that American Invsco had circumvented county condominium laws requiring that tenants be notified of the building's sale and given 150 days to form an association and buy the building at the same price.

County condominium laws, passed in January after a four-month conversion moratorium expired, were enacted after an estimated 20 percent of the county's apartment units had gone condo.

Restrictions on co-ops were not included in the original legislation -- because Gilchrist felt the infrequency of co-op conversion in Maryland indicated there would be no problems with this form of housing.

County officials, however, contend that what they view as a usurpation of tenant protection laws will not be tolerated.

Gilchrist asked the council last week to enact emergency legislation setting a nine-month moratorium on co-op conversions and the sale of memberships in such conversions.

While conceding that condoiniums and cooperatives represent two distinct legal entities -- tenants own their unit with a condominium, whereas they buy shares in a corporation with a cooperative -- Gilchrist said that for the tenant the practical effects are the same: higher monthly payments, displacement, and increased anxiety. Therefore, Gilchrist insisted, the intent of the law -- to protect tenants -- should be honored whether the conversion is condominium or cooperative.

Gilchrist's assurances, however, have done little to quell the fear of most Promenade residents -- many young and single professionals who have opted for the amenities luxurious apartment living affords without the burden of homeownership. Based on past performances, American Invsco is a formidable -- and seductive -- opponent.

Last year, when American Invsco converted the Grosvenor Apartments across the street into condominiums, company officials served breakfast every morning for months and threw several exravagant tent parties to woo tenants.

"They come on like gangbusters, said Peter Messitte, attorney for the Grosvenor tenant association.

Ironically, Anne Solator, president of the Grosvenor tenant association during the conversion and once known as one of the most adamant opponents of conversion, is now employed by American Invsco as a customer relations employe.

These days, Solator can be found in the Arcade -- a cluster of shops, beauty salons and restaurants in the Promenade -- assuring tenants of American Invsco's "good intentions."

"I know what it's like to be a tenant faced with conversion," Solator said, "I can help the tenants overcome their fear."

Asked to explain her switch in allegiance, Solator explained that the emotional stress of the conversion initially played an overriding role in her resistance. Once the emotional tide had subsided, intentions became clearer and Solator said she "grew to have great respect for the company."

"I am paid for being concerned," Solator insisted, "I wouldn't work for a company that didn't allow me to care. I am the same person I was last year."

Tenants have been given until Sept. 1 to decide whether they want to purchase their apartments. After that date, American Invsco says it will begin selling the units, with occupancy when current leases expire.

American Invsco completed its purchase of the Promenade three weeks ago for $54 million but did not announce the sale until last week. It announced the conversion to co-ops at the same time.

Last Friday each tenant received another letter setting the price a non-resident would pay for his unit. But on Saturday, when company officials began telling residents individually how much the units would cost, the prices they were quoted were considerably higher in at least half a dozen instances, according to tenants.

Frieda Saltz, for example, was initially told the price of her one-bedroom apartment would be $71,514. But when she saw company officials last weekend, she was told the price would be closer to $92,000.

Saltz also was told that her montly payments, if she bought a co-op, would average $1,200 a month. She now pays $415 in rent.

Company officials will not discuss the discrepancy in prices, saying they will talk only to the individuals involved.

All Saltz really wants to talk about, though, is how the conversion can be stopped.

"I will do anything to help -- stuff envelopes, staple, deliver," said Saltz, 68, a lithe woman finely garbed in white knit and pearls. Someone, she said, "has got to protect us 'graysters.'"

Saltz, a widow who moved two years ago to the Promenade from Los Angeles to be closer to her two daughters in Montgomery County, reflects the feelings of despair and anxiety felt by many of the older residents.

"I moved here," Saltz said, focusing on the women surrounding her, "because I felt that at my age I needed to move somewhere I could stay put. I have made close friends here."

If the conversion proceeds, Saltz said, she could not buy her unit. Living off social security and interest from money left by her husband, Saltz said she had no extra money for a down payment.

"The whole situation is very sad," Saltz said. "I wake up all the time wondering what's going to happen."

American Invsco officials said elderly residents would most likely be able to remain at the Promenade for two years without purchasing.

The chances are good, however, that the conversion to co-ops will be delayed. The legislation proposed by Gilchrist calls for a nine-month moratorium on any co-op conversion in the county. The council will begin considering it at a July 21 hearing.

If the moratorium is passed, Gilchrist is expected to present legislation that would apply the same restrictions on co-op conversion as now exist on condominium conversion.