If that forest of antennas on top of the Soviet Embassy on 16th Street looks suspicious, there's a good reason for it. It's true that none of the dozen or so antennas appears to be state of the art or anything remotely close to it, and that the most imposing of the antennas, the low-frequency, log-periodic affair that hangs over the embassy's roof like a denuded umbrella, turns out to be standard issue for embassies, used for overseas radio transmission and reception.

But what about the rest of it?

Here are two versions of what's going on--one innocent and one sinister. The innocent version is that the Soviets are like everyone else. They like a good show and simply watch a lot of television, enjoy FM music and tune in every now and again to the District police and FBI radio communications.

Although the equipment on the Soviet Embassy roof seems unsophisticated, there is the sheer volume of it--12 different antennas:

* one omni-directional high-gain (short-range radio);

* one standard FM radio;

* four log-periodic (standard) VHF television;

* two microwave (one is for Home Box Office--the embassy is a subscriber; the other antenna's purpose is unknown);

* one log-periodic, low frequency for long-range (international) radio transmission and reception;

* one rhombic for long- range (international) radio transmission and reception;

* two ultra high frequencies. (One of these UHF antennas is aimed in the general direction of Super TV's transmitter in Northeast Washington, but the embassy is not listed as a subscriber.)

Assume that one of the microwave HBO-type antennas is being used for HBO. What is the other one being used for? It's aimed in the general direction of Foggy Bottom, McLean and the Pentagon. And what about the other UHF antenna--the one not aimed at Super TV--facing the same direction as the mysterious microwave?

Under the innocent scenario, the second microwave antenna is for C-SPAN, the public affairs subscription service, which televises proceedings of Congress and the like. The only problem is that the embassy is not listed as a subscriber to C-SPAN, so if the Soviets are tuning in to it, they're pirating the signal.

And if they're not watching C-SPAN, then what are they watching?

Enter the second, more sinister version. One authoritative analysis holds that with some combination of antennas, they're listening to any phone call they can tune into, especially government calls where the parties may forget (or not realize) that they're talking on an insecure line. The conversations are taped and then shipped back to Moscow for analysis. Some portion--Ma Bell can't say how much because the routing is done by a computer-- of Washington's incoming and outgoing long distance calls are handled via microwave or satellite, where they are easily accessible for eavesdropping by anyone with the proper antenna (hint).

According to a Soviet Embassy spokesman, the antennas were installed under a bilateral agreement with the United States with the advice and cooperation of the State Department. "The simple purpose of the antennas is to maintain radio communications with Moscow," the spokesman said, declining to answer questions about antennas that were unsuitable for anything but short-range communications.

"If they're using them for television reception," an American official said, "they're doing an awful lot of television watching."