WASHINGTON (AP) _ As President Clinton was forced by knee surgery to postpone for 24 hours his summit with Boris Yeltsin, the Russian president made clear today that Clinton should come prepared for tough exchanges in their two days of talks.

In remarks to reporters in Moscow, Yeltsin today criticized NATO's plan to expand eastward and urged Clinton to make concessions ``in order to preserve our partnership.''

``Our diplomats have made enough concessions to the United States,'' Yeltsin said. ``We can't give any further. Now, it's the U.S. turn to move in order to preserve our partnership.''

Yeltsin responded sharply when asked if Russia feared NATO's military might.

``NATO won't dare attack us, it's not that I fear,'' he said. ``I fear a Western blockade of Russia, which we can't allow.'' He added, ``We have a sufficient deterrent force, including nuclear (weapons).''

Clinton was meeting at the White House today with Russian Foreign Minister Yevgeny Primakov for a pre-summit discussion of these and other ticklish issues.

Primakov went over those topics Saturday with Secretary of State Madeleine Albright and again Sunday with Defense Secretary William Cohen at a meeting held at Primakov's request in the ``tank,'' the Pentagon's secure briefing room. It was unclear what, if any, progress had been made.

At Clinton's request, Yeltsin agreed Sunday to delay their summit in Helsinki, Finland, by one day _ to Thursday and Friday from Wednesday and Thursday _ to give Clinton extra time to recuperate from his knee surgery.

Just a few weeks ago, many in Washington doubted that Yeltsin was healthy enough to meet with Clinton. Yeltsin was so weakened by pneumonia in January, after heart surgery in November, that the summit was changed from Washington to Helsinki to save him a long trip. His recuperation has since accelerated.

Thus, it may have given Yeltsin puckish delight to tell Clinton in a get-well telegram that he was ready to meet him ``as soon as your health allows.''

Clinton's state visit to Denmark, originally scheduled for Friday, has been postponed until July. Clinton told reporters he hopes to fit in that visit while in Europe to attend a NATO summit.

In Moscow, the Kremlin press service announced the summit was pushed back a day ``by mutual agreement'' and said the delay was made necessary by Clinton's recovery from surgery to repair the tendon he tore Friday in Florida.

White House spokesman Mike McCurry said the decision to delay the summit's start by 24 hours was made Saturday night by Erskine Bowles, the president's chief of staff, and the National Security Council staff.

``It gives the president an additional day to convalesce and an additional day to learn to be mobile,'' McCurry said. The trip begins Wednesday night.

Asked whether the summit's schedule of meetings had been shortened, McCurry made a veiled reference to the earlier worries over Yeltsin's health.

``Remember,'' he said, ``the schedule had been designed to accommodate everyone's health needs.''

Doctors said Clinton will be in a wheelchair for several days and on crutches for about eight weeks as he recuperates from Friday's knee surgery. In addition to the regular three-person medical team that normally travels with him, an orthopedist and a physical therapist will accompany him to Helsinki.

Even before going into surgery, Clinton pledged not to let his injury stop him from attending the Helsinki summit, where an unusual mix of tough and sensitive topics will be discussed, including NATO's plans to expand eastward.

Clinton considers NATO expansion his top foreign policy priority _ linked to other festering security issues such as overcoming the Russian parliament's reluctance to ratify the START II nuclear weapons treaty.

Yeltsin said in an interview published Sunday in Finland's leading newspaper, Helsingin Sanomat, that Finland should not think of joining NATO. The Russians already have made a fuss over the Western alliance's intention to invite some former Soviet-bloc nations _ probably Poland, Hungary and the Czech Republic _ to join.

``To us, bringing the alliance's military infrastructure closer to Russian territory is absolutely unacceptable,'' Yeltsin said in the Finnish interview.

McCurry said Clinton was aware of Yeltsin's remarks and viewed them as a reflection of Russia's well-known objections to NATO expanding eastward.

In the past week, McCurry and other Clinton aides have voiced optimism that the summit will bring the two sides closer on that thorny issue.