Ailing Chrysler Corp. yesterday officially announced $400 rebates on most of its cars and trucks beginning today in a bold bid to lift sagging sales.

A company announcement said the rebate offer would apply to all 1979 models except popular Plymouth Horizon and Dodge Omni models, already in short supply, and the cars and trucks the company imports for sale from Japan.

Coming on top of previously announced dealer incentives allowing price discounts of up to $1,000 on some Chrysler models, the rebates represent a determined -- and potentially costly -- effort by the troubled No. 3 automaker to sell-off bloated inventories and recover from a record $260 million first half loss.

In related development yesterday, Chrysler began placing full-page ads in newspapers and magazines across the country to win public support for its bid for federal aid. The ads state that Chrysler is not asking the government for a "handout, a bailout or welfare" but simply help in meeting short term expenses induced by government regulations.

The company has put that cost at $1 billion. Though it asked for cash credits now against future tax payments, Carter administration officials rejected that plan and proposed instead to ask Congress for loan guarantees of up to $750 million.

The advertisement headed "Would American Be Better Off Without Chrysler?" conceded the company had "made our share of mistakes in a tough competitive business. And we're willing to accept responsibility for them." But the text went on to say that to refuse to support Chrysler would result in the "irresponsible" abandonment of many employes, communities and supplier companies.

The Detroit Free Press reported that Chrysler was about to sell some of its dealership land and buildings around the country to an unidentified buyer for $50 million.

The property in question is handled by Chrysler's real estate unit, a subsidiary that owns or leases 787 of the 4,700 dealerships. The company said it had "nothing to report" on the matter.

In Washington, United Auto Workers President Douglas Fraser met with Treasury Secretary G. William Miller to argue that the government buy shares in Chrysler. After the meeting Fraser reported, "They listened respectfully. The government hasn't ruled out anything, but obviously they're leaning toward loan guarantees."