U.S. envoy Reginald Bartholomew, who has been negotiating the future of American bases in Greece with the Socialist government of Prime Minister Andreas Papandreou, will return to Washington this weekend for about two weeks of consultations, the U.S. Embassy confirmed today.

Announcement of a final draft of a bases agreement, after eight months of negotiations, had been widely expected earlier this week, but an apparent last-minute hardening of position by the government in Athens resulted in rejection of the draft accord as too moderate and new proposals being submitted to Washington.

Bartholomew met with his Greek counterpart, Foreign Undersecretary Yannis Kapsis, yesterday and received from him a document outlining Greece's position on the bases, according to a Greek government spokesman.

Papandreou told the Greek Cabinet last Friday that the talks would end this week. Although he said he did not know "which way the scales would tip," diplomatic observers here expected the government to initial a new bases pact.

The government set the stage Tuesday for announcement of the conclusion of the negotiations, planning political and press briefings as well as a nationally televised messsage by Papandreou.

Analysts link the Socialists' about-face with stormy reaction from the Greek left to leaked reports of the proposed agreement in the influential Athens newspaper To Vima on Sunday.

The reports--not denied by either Greek or U.S. sources--said the accord would have a five-year term. It would contain provisions for termination but also for renewal by whatever government is in power in Greece at the expiration date.

This would place the decision on whether to close the bases, which Papandreou has pledged to do, well beyond the end of the present Socialist government's term in 1985. The Communist press called the leaked agreement a "document of shame."