In a coincidence of good timing, Public Broadcasting Service stations on July 23 will televise the documentary "Roses in December--the Story of Jean Donovan." A few days later, on July 28, the Reagan administration must certify improvements in El Salvador's human rights as a congressionally required condition for continued military aid.

The two events are connected. Jean Donovan was one of the four American churchwomen slain in El Salvador on Dec. 2, 1980. Some low-level hit men from the armed forces have been arrested, but they have not been brought to trial. No higher-ups have been fingered. An effort is being made in Congress to block money for military aid to the violence-prone Salvadoran government until the case is settled.

The power of the PBS documentary is that it may reshock us into remembering United States complicity in the siege of death in El Salvador: Our government arms a government that kills Americans.

Jean Donovan went to El Salvador under the sponsorship of Archbishop James Hickey, then of Cleveland. She contributed as an individual what her government should have been giving collectively: gifts of caring to the rural poor whose destitution is at the core of Salvador's enduring darkness. Donovan embodied the ideal that has been the force prompting every humanitarian--from Maryknoll missioners to Peace Corps volunteers--who has gone to Latin America to share his unearned blessings with those who have few.

Salvadoran poverty tends to be overlooked in the policy debates. Nearly three-fourths of the children are hungry. A majority of citizens is landless. What little natural wealth there is--coffee, cotton, beef--is exported.

In the PBS documentary, Donovan is shown praying over the casket of Oscar Romero, the archbishop who pleaded with the United States before his assassination in March 1980 to stop sending military aid to a Salvador government corrupted by right-wing army officers. The Carter administration, backed by Congress, refused the request.

Now, two years later, with the killing continuing at the rate of 250 people a week and most of the terror committed or sanctioned by security forces, the case for cutting off military aid is stronger than ever. A new power in Salvadoran politics is Robert D'Aubuisson, the admirer of Hitler whose ties to death squads were of such blatancy that two years ago he was banned from entering the United States. He was kicked out when he sneaked in anyway. Now the Reagan administration says this punk is welcome to visit Washington to discuss policy.

The repugnance for D'Aubuisson serves at least one purpose: the end of the illusion about America's military aid. We were told by Reagan officials that a militarily strong government was needed to beat down the insurgents. When it came out that the militarily strong govenment was killing women, children, old people, priests, nuns, labor leaders, journalists and Jean Donovans as well as insurgents, it was said that the people would speak through the March elections and thereby control the military.

But that didn't happen. Gen. Jose Guillermo Garcia was the unelected defense minister who oversaw the military repression before the election and he oversees it now. As long as Gen. Garcia or his kind of policies dominate El Salvador, no chance for peace exists.

For the United States, a policy of illusion--that El Salvador's leaders will begin to behave once they have more weapons--has evolved into a policy of deceit--that the armed leaders are behaving now. No evidence supports the view that D'Aubuisson has gone from death squads to life squads, or that land reform programs are working, or that we are any closer to settling the murders of the four churchwomen. A report last January by Reagan officials that progress in human rights was being made, and therefore El Salvador was entitled to continued military aid, has been found by the American Civil Liberties Union to be unbacked by any reliable research.

As Archbishop Romero knew 28 months and 28,000 deaths ago, more military aid leads, logically and tragically, to a bigger war against a poorer people.